The Hatch estate at Mersham had belonged to the church since 1051, but was purchased by the Knatchbull family in 1486. Sir Wyndham Knatchbull-Wyndham, 6th Baronet (1737-63), succeeded his father in 1749, he served as MP for Kent in 1760-63, and was a subscriber to Adam's Ruins of the Palace of the Emperor Diocletian at Spalatro in Dalmatia, published a year after his death, in 1764. He died unmarried, and the title reverted to his uncle, Sir Edward Knatchbull, 7th Baronet (1704-89). Sir Edward was the third son of the 4th Baronet, but nonetheless succeeded his nephew in 1763, prior to which he had served as MP for Armagh Borough in the Irish House of Commons in 1727-60.

Hatch House was started by Sir Wyndham in 1762, and completed by his uncle, Sir Edward, in 1772. It was the first completely new house built by Robert Adam, but it is important to note that drawings among the Arundell and Wardour papers in the Wiltshire Record Office provide evidence that Robert Mylne (1733-1811) provided earlier, unexecuted designs for the house in 1761. Adam himself made two sets of plans for the house: the first scheme being for a square, three-and-a-half-storey house, and the second, more impressive scheme, with a two-and-a-half-storey central block flanked by wings was executed. The house was built on a slope so that the half-sunk basement on the principal (south) front is at ground level on the garden (north) front.

Adam's house was simple, with no portico, and very little Portland stone dressing. According to Bolton this shows a large family house parsimoniously built. Pevsner described Sir Edward as 'tight with his money', and the total cost of the house was only £20,000. Indeed, the relatively stark principal (south) front is similar to that at Dumfries House, designed in 1754 before Adam had left Scotland for his Grand Tour.

There are various drawings for the interior of the new house in the Adam drawings collection at the Soane Museum, but it is doubtful if all of the ceilings were executed. Those for the hall, drawing room, and dining room certainly were executed, although the dining room ceiling was slightly altered in execution, and the hall ceiling was demolished during the twentieth century. According to Pevsner and Newman 'only the ceiling of the bow-ended drawing room has the full characteristic Adam flavour'. The plasterwork on these ceilings, and elsewhere in the house was by Joseph Rose (1744-99), the decorative paintings by Antonio Zucchi (1726-95), and the chimneypieces were carved by Thomas Carter (d1795).

A stone loggia was added to the bow on the garden (north) front of the house in 1872 by James Piers St Aubyn (1815-95), and he also turned two rooms into a library. In 1952 the house was Grade I listed, but a portion of the park was sold in 2004, with part being opened to the public, and part being used as a business village.

See also: St John the Baptist's (Lady Chapel), Mersham, Kent, Monument to Sir Wyndham Knatchbull-Wyndham, 6th Baronet

Literature:
A.T. Bolton, 'Mersham Hatch, Kent: the seat of Lord Brabourne', Country Life, 26 March 1921, pp. 368-75; A.T. Bolton, The architecture of Robert and James Adam, 1922, Volume II, Index pp. 17, 78; N. Pevsner, and J. Newman, The buildings of England: west Kent and the Weald, 1976, pp. 425-26; J. Ingamells, A dictionary of British and Irish travellers in Italy: 1701-1800, 1997, p. 581; D. King, The complete works of Robert & James Adam and unbuilt Adam, 2001, Volume I, pp. 113-15, Volume II, p. 126; A.N. Newman, 'Knatchbull Wyndham, Sir Wyndham, 6th Bt. (1737-63), of Mersham Hatch, Kent', History of Parliament online; 'Mersham Le Hatch, Mersham', www.britishlistedbuildings.co.uk

Frances Sands, 2012