The history of the design of Holkham Hall in Norfolk has both captivated and baffled commentators and architectural historians ever since the death of the house’s great creator Thomas Coke, 1st Earl of Leicester, in 1759. In more recent times Professor Leo Schmidt has advanced the suggestion that the origins of the design did not lie, as had been commonly thought, in the period immediately before construction is known to have begun in 1734, but rather in 1726 - when Coke made a payment to his executant architect, Matthew Brettingham the Elder, ‘for drawing a Plan of a New House’. Schmidt believes that ‘Plan’ should be identified with a set of drawings in the British Library, which he has denominated ‘Holkham 1’ (Fig. 1). They show the central block of the house much as built, though without its four wings and with an attic floor externally expressed on all fronts except the north. Schmidt subsequently credited the origination of this design to Colen Campbell who, he discovered, had also been employed by Coke in 1725-26. The elapse of time between 1726 and 1734 may not seem very great but, as is well known, this was a key period for the formulation and development of Palladianism in Britain so that the issue of date here is of considerably more than local significance. Indeed, as John Harris has written of Schmidt’s intervention on the question of Holkham’s date, ‘it is absolutely critical for the history of neo-Palladianism to get this right.’ Holkham shares many features in common with Richard Boyle, 3rd Earl of Burlington’s indubitably innovative Chiswick House, and, were ‘Holkham 1’ really to date from 1726, that would make the Norfolk building the fraternal (indeed perhaps first-out) twin of Chiswick rather than its part progeny, and consequently a building of seminal importance for the history of British architecture rather than a stellar and much developed example of an idiom already initiated elsewhere.