Leicester House (act. 1743–1760), is the name given to a changing cast of politicians and courtiers gathered around Frederick Lewis, prince of Wales, and after his death in 1751 his widow, Augusta, and their son George, who in 1760 succeeded to the British throne as George III. The name is derived from Leicester House, the London residence of the Sidney earls of Leicester on the north side of the modern Leicester Square. This house was rented by Frederick from 1743, which is the year taken here as the start of Leicester House as a political grouping, though the term is often used to refer to Frederick's political circle before this date. To add further confusion, Frederick's parents, George II and Queen Caroline, resided at Leicester House before their accession to the throne, and they and their followers between 1717 and 1720 are also sometimes described as the Leicester House party. While membership of Leicester House during the 1740s and 1750s was not constant, as political allegiances were renegotiated several times, the group's activities had a lasting legacy on parliamentary opposition in British political life and on attitudes towards the conduct of government and its personalities during the early part of the reign of George III.

Frederick's role as the focus of opposition was in part a function of the parliamentary monarchy established following the revolution of 1688–9. The monarch remained the source of patronage and exercised executive authority, particularly over the armed forces and foreign affairs; expenditure needed the approval of parliament and members of the Commons and Lords competed to act as managers of parliament for the monarch, at the same time ensuring that the policies of the executive reflected opinion in the Commons. Politicians out of favour with the existing monarch and his ministers often gravitated towards the next heir to the throne, threatening the incumbent ministers with sudden removal should the monarch die. With the heir as an ally, opposition politicians could convincingly formulate a politics that countered accusations of disloyalty to the protestant succession through championing the heir as an alternative focus of fidelity to the reigning dynasty.

When Frederick moved to Leicester House he was politically aligned with his father, George II, and the ministry led nominally by the earl of Wilmington but in practice dominated by John Carteret, second Earl Granville, and by Henry Pelham. Frederick's principal political adviser was his secretary, George Lyttelton, alongside his clerk of the closet and chaplain, Francis Ayscough. Other members of the parliamentary Leicester House group at this stage included Charles Calvert, fifth Baron Baltimore; Frederick's treasurer of the household, Thomas Lumley Saunderson, third earl of Scarbrough (c.1691–1752); Frederick's vice-chamberlain, Sir William Irby (1707–1775); Frederick's cofferer and surveyor-general, Lord Archibald Hamilton (1673–1754); Thomas Pitt (c.1705–1761), who held office from Frederick's duchy of Cornwall as lord warden of the stannaries; Frederick's chancellor, Thomas Bootle (1685–1753); the clerk of the household Charles Hamilton, brother-in-law of Lord Archibald Hamilton; and grooms of the bedchamber Sir Edmund Thomas (1712–1767), John Evelyn (1706–1767), and Thomas Bludworth (d. in or after 1772). Frederick's political advisers also included his wife's groom of the stole and mistress of the robes, Lady Jane Hamilton (d. 1753), who was Lord Archibald's wife and was also recognized as the prince's official mistress. Other politicians might have divided loyalties, such as Sir Charles Wyndham, who had been brought into parliament as an ally of Frederick but also cultivated links with Granville. In 1744 George Lyttelton left Frederick's household to align himself more closely with Henry Pelham's administration; other supporters and allies such as Hamilton and Wyndham chose to stay on the government side of the Commons when Frederick decided to go once more into opposition before the election of 1747.

The political complexion of Leicester House thus changed. Frederick's political declaration—named after one of his other residences, Carlton House—invited the participation of the tories in an enlarged and co-ordinated opposition. This had the effect of reviving the patriot principles of the opposition of the late 1730s and early 1740s (as articulated with most conviction and consistency by Cobham's Cubs) against the old corps whigs of Henry Pelham and his brother the duke of Newcastle, depicted as corrupt ministers from whom Britain had to be rescued. Frederick's circle had already included some tories such as Charles Edwin (c.1699–1756), whose wife Lady Charlotte Edwin (d. 1774), a niece of Lord Archibald Hamilton, was a lady of the bedchamber to Augusta from 1737. But he now secured the co-operation of independent politicians like Sir Francis Dashwood, as well as ambitious whigs disenchanted with the Pelham ministry and hoping to profit from attachment to the king in waiting. Most prominent of these was John Perceval, second earl of Egmont, who became Frederick's principal political adviser after the election of 1747. George Bubb Dodington, who had advised the prince during the 1730s, returned to Frederick's side at this point.

Other member of the new inner circle were George Lee, who played a role in co-ordinating Frederick's political activities alongside Egmont, and Sir John Cust, who became the prince's clerk of the household. William Talbot, second Baron Talbot of Hensol (1710–1782), was one of Frederick's intermediaries with potential supporters, as was Francis North, seventh Baron North. Egmont's undated prospectus for the formation of a new administration on Frederick's accession to the throne reveals Henry Howard, fourth earl of Carlisle [see under Howard, Charles third earl of Carlisle], as Frederick's choice to head a ministry with a prominent role for Sir John Willes (as lord chancellor). The proposed ministry was to have been a coalition between Frederick's supporters, selected tories, and some ministerialists. Baltimore would have retained his government position as a lord of the Admiralty, and other friends of Frederick to have been included were Charles Sackville, earl of Middlesex; Henry Brydges, second duke of Chandos (1708–1771); Henry Bathurst, whose father Allen Bathurst, first Baron Bathurst, was a veteran of the Oxford ministry under Queen Anne; and John Fane, seventh earl of Westmorland, whose support for Frederick was a contingency following his earlier advocacy of a Stuart restoration. Sir Henry Erskine of Alva and Cambuskenneth represented a connection between Frederick and the party of the duke of Argyll, the dominant whig interest in Scotland. Pitt and Ayscough remained in charge of the detail of electoral management. A newspaper, The Remembrancer, was founded in 1747, edited by James Ralph.

The death of Frederick in March 1751 brought a contraction of the Leicester House group and the diffusion of its political focus. Some of his allies sought at first to pursue a coherent strategy: Westmorland, for example, financially supported The Remembrancer for a few months after Frederick's death, although it closed in June 1751. In practice, though, most of the prince's leading supporters sought rapprochement with the government. Thomas Pitt mortgaged his electoral interest to the court to raise a pension to cover his debts, and gave up opposition. Dodington returned to support Pelham. Lee held posts from the court and from Augusta. Henry Bathurst chose to concentrate on his legal career. Cust became clerk of the household to the princess, but supported Pelham in the Commons. Egmont was isolated as an opposition adviser to the dowager princess of Wales, who was herself dependent on the goodwill of George II. Meanwhile tories, such as Velters Cornewall (1697?–1768), whose wife was a member of Augusta's household, maintained contacts with Leicester House.

A reinvigorated Leicester House began to emerge about 1754. One of the minor members of Frederick's circle had been John Stuart, third earl of Bute, a lord of Frederick's bedchamber from 1750. Bute had not been greatly involved with politics during Frederick's lifetime, but his apparent disengagement from parliamentary factions became an asset to Augusta when she became frustrated with the limitations of James Waldegrave, second Earl Waldegrave, as governor to her son George, prince of Wales, by 1754. Bute was able to overcome the prince's introverted nature and enable him to make progress in his studies, and when in 1756, at eighteen, the prince became too old to have a governor, Bute became his groom of the stole, recognizing that he had enjoyed the greatest share in forming the prince's mind and that the prince was happy that he should continue to have a similar role into the prince's adulthood.

While serving as the prince's governor, Bute began to nurture the reversionary political interest, aligning the prince's court with William Pitt from 1755 in opposition to the duke of Newcastle and Henry Fox and their advance towards a renewal of war with France and subsidies to Hanoverian troops. With Pitt came another discontented former ministerialist, Henry Bilson Legge; and George Sackville [see Germain, George Sackville], a young army officer and MP hoping for preferment when George should succeed to the throne. Some of the old Leicester House opposition, such as Cust, returned to voting against the government, but this realignment around Pitt edged out Egmont's remaining claims to political leadership at Leicester House. However, the momentum shifted again in November 1756 when Pitt became secretary of state in an administration headed by the duke of Devonshire, which also contained Legge and Sackville; this was then replaced the next year by a stronger administration in which Pitt joined forces with Newcastle, the very minister he had been set against. Bute was left conducting a forlorn opposition from Leicester House. Bute and Prince George subsequently regarded Pitt as a traitor.

As well as political preparations, Prince Frederick's opposition had been a source of cultural patronage, including the commissioning of the opera Alfred from Thomas Arne, James Thomson, and David Mallet before the move to Leicester House took place. Bute ensured that there were plays alluding to a glorious patriot future under his charge, Prince George. By 1755 he had met John Home, a Church of Scotland minister and playwright, and encouraged or collaborated with him in the writing or revision of Agis (1754), Douglas (1756), and The Siege of Aquileia (1759) in order to associate Prince George with the triumph of public virtue over a debased self-interest that Bute associated with the court and governments of George II. Douglas, which was performed in London first, was highly praised, but Agis was widely perceived as simplistic political propaganda (though Prince George saw it three times). However seriously Bute and George took its message, the wider political world was apt to interpret it as hollow cant.

The final years before the accession of George III seem to have seen the end of an effective Leicester House party as such. Pitt had used the Leicester House connection as leverage to force his way into government and inject patriot political language into the coalition with Newcastle he formed in 1757; this, and the ongoing Seven Years' War, contributed towards the reduced opportunity for a co-ordinated Leicester House opposition. Political leadership at Leicester House was monopolized by Bute, Cust and Lee having resigned from their posts in the princess's household in 1756 and 1757 in protest. One veteran supporter of Frederick who returned to Leicester House in 1756 to join Prince George's household was John Evelyn, still MP for Helston in Cornwall, to which he had been elected on the prince's interest in 1747, though Bute regarded him as a supporter of Newcastle. Another long-standing member of the Leicester House court, Bludworth, retained his office as commissioner of the horse, managing the princess's stables, but appears to have given up all further parliamentary ambition. Sir Edmund Thomas was clerk of the princess's household from 1756, and joint treasurer from 1757, but had left the Commons in 1754, and was in any case of little influence outside his home county of Glamorgan, where he helped Lord Talbot of Hensol organize an opposition interest in the late 1750s. More loyalty, perhaps, was shown by Scottish connections of Bute, such as William Douglas, third earl of March. The last serious attempt at a propaganda coup was probably the unsuccessful attack on St Malo, mainly conducted by army officers close to Bute and Prince George, in 1758. Even so a Leicester House interest endured to the decade's close, as politicians within the ministry and among its supporters maintained connections with the future king and his adviser without going into formal opposition. During the 1750s the ministry offered encouragement to tories, partly because this suited William Pitt's patriot rhetoric, and partly because the leadership of tory families was passing to younger men who had grown up entirely within the period of whig dominance. None the less many tories saw paying court to Leicester House as a more certain route to promotion, aware of how the old corps whigs had betrayed them in the 1740s during the broad-bottom ministry. On becoming king, George III was able to fulfil tory expectations by rewarding some of the party's leaders with household appointments and allowing tories to join commissions of the peace, fulfilling an old Leicester House promise.

The accession of George III ended the Leicester House connection. Bute became a privy councillor, secretary of state, and eventually prime minister in 1762, resigning the next year. Various former supporters of Frederick were rewarded with office or peerages, including the faithful Sir William Irby, who became first Baron Boston, and Egmont, who received his coveted British peerage as Baron Lovel and Holland. Augusta, dowager princess of Wales, moved out of Leicester House itself in spring 1764; her son Henry, duke of Cumberland, remained there until 1767, when the royal connection ceased. The demise of the political Leicester House did not end critics' interest in the supposed existence of patriot or tory networks, now at the centre of British politics. The reconstruction of the political élite, and the rise of Bute without obvious support, led to a suspicion throughout the first two decades of the new reign that the king's former tutor exercised secret influence through his friendship with the king and through a network partly derived from his time at Leicester House, the group identified by contemporaries as the king's friends.