Work on the first phase of this ambitious masterplan is the East Wing project. Building work will start next March and will be complete by November 2004. It will re-open a long-sealed original door, east of the central portico at street level, taking the public through to a grand new modern daylit atrium with staircase and lift, made from an existing - but unused - internal courtyard. In addition, a new lower hall will act as a meeting-point and will contain touch-screen computers displaying the entire National Gallery collection.

On the floor above, the existing cramped central portico entrance lobby will be opened out by removing dividing walls. Beyond that, the staircase hall will be restored to its original Victorian appearance, and the central hall behind - at present a meeting-point hung with inferior pictures - will be upgraded to a proper airconditioned gallery.

First drawn up under the Gallery's previous director Neil MacGregor - now at the British Museum - the project has been stimulated by the arrival of new director Charles Saumarez Smith, who previously built the successful new Ondaatje Wing at the neighbouring National Portrait Gallery.

Removing vehicles from the north side of Trafalgar Square, where the Gallery sits, has also given impetus to the scheme. Delayed for years by bureaucratic wrangling but finally forced through by London Mayor Ken Livingstone, the resulting Norman Foster-designed piazza in front of the gallery is now being built. With its great new flight of steps leading directly down into the square, it will be complete by spring 2003. This will give the gallery the necessary elbow-room to open up at ground level onto what were previously only narrow pavements.

Architects and masterplanners for the National Gallery are Sir Jeremy Dixon and Edward Jones, designers of the NPG's Ondaatje Wing, the rebuilt Royal Opera House in Covent Garden, and the new fountain court at Somerset House. The East Wing project is just the start. Dixon and Jones have also designed a mirror-image second phase in the Gallery's West Wing, this time using an existing original western entrance at ground level and a second former courtyard. After that, attention will turn to the rest of the neglected lower regions in the rear half of the building, which at present is a rabbit warren of offices and stores. The plan is to make a new central spine of lower galleries running all the way from west to east sides of the building, replicating the shapes of the existing galleries on the main floor above. This new sequence of galleries will be daylit by opening up more old courtyards.