Just as cramped old theatres always need big new foyers, so do museums. People need to mill about. They like to find their restaurants, bars and cafes and shops, and they expect a reasonable amount of space when they do. And from the point of view of the museum, it's vital. If people swarm around all these offerings, they will pause and buy. Indeed, they will go there precisely in order to buy. People go to restaurants at art museums who never bother to glance at the art. So more people come in, the cash tills ring out, everybody is happy. Because you don't have to buy if you don't want to. It's not an admission charge. At the National Gallery, you can march in, get your fix of Cuyp or Constable, and march straight out again, hands firmly in pockets. And drink your coffee from a Thermos in Trafalgar Square.

So what does the National Gallery's new East Wing do for the average gallery-goer who does want to look at the art, but wouldn't mind some creature comforts at the same time? Essentially they remove a bottleneck - the pinched foyer of the old building sandwiched between the outside flight of steps leading up from the Square, and the inside flight of steps continuing on up to the main gallery level. That old foyer remains - and will be a revelation when it is shortly both opened out and restored - but much of the pressure of four million visitors a year is taken off it by the new entrance. Which also happens to be a very old entrance, a big door to what was once a carriage-way through the original building to a workhouse and barracks behind.