Typical of Ed Jones, however, to point out the inspiration behind the design of the National Gallery's east atrium. Sir Edwin Lutyens' Staircase Court from Viceroy's House in New Delhi? At first, you wonder what possible connection there could be between the two spaces. Then Jones pulls out his book on the palace and opens it at the key photo. Yes, the parti is the same: the staircase up one side, the balcony level overlooking the court, the light flooding in from above, the upper-level doorway through to the rest of the complex beyond. A near-perfect model. However, in his proposed new austerely-stripped version for the National Gallery, the opening to the sky is more reduced than the Lutyens example. A sharply-angled roof lantern, its sides closing in, leaves a rectangular strip of glazing at the top. The ETFE foil proposed for this will, promise the architects, be sufficiently transparent to see the sky and clouds over London, without the light-filtering baffles that are necessary in gallery spaces.

It is too easy to say that this is the project that the National Gallery should have had up its sleeve ready to tap the National Lottery with in the mid 1990s, when £100m-plus projects were feasible in one go. But back then, the Robert Venturi-designed Sainsbury Wing at the western end of the complex was still comparatively new, the culmination of a long and wearying saga. The feeling was that restoration of the original galleries was the main task in hand, and this has now been done. Previous director Neil MacGregor also felt strongly that Lottery cash was better spent on pictures than buildings - such as Stubbs' awe-inspiring rearing-horse portrait "Whistlejacket". When you see it, you can't help thinking he was right.

So - despite the general tightness of finance - now is philosophically the right time to begin the National Gallery's mighty revamp, with a new director who is used to building, and who has a high opinion (and direct experience) of his architects. Some are already saying that this could be the best work that Dixon and Jones, both now over 60, ever do. With all its phases, it will certainly keep them occupied for a long time. Indeed their masterplan may eventually be completed by other architects, under another director. They are prepared for that.