Closing off the north side of the square to vehicles, so creating a broad terrace in front of the National Gallery, is a boon. That's the paving - nice big stone slabs. Then this terrace is connected down to the square below via a broad flight of stone steps which did not previously exist, on axis with the central portico of the National Gallery. Apart from a pair of discreet bronze-framed glass lift boxes placed either side of the steps for disabled access, and some rather horrible blobby benches, that's the extent of the visible design. The rest is all down to the way the traffic now flows round three sides of the square instead of four. It's a relatively complex thing to work out, but it is standard stuff, the bread-and-butter of highway engineers everywhere.

The changes made to the physical fabric of the square may be minor, but they give the place a strangely unbalanced air. Nelson's column with its four Landseer lions at the southern end forms a triangulated composition with the two great fountain pools by Sir Charles Barry with their Lutyens centerpieces, set on what was the half-way line of the square. Now that a great big staircase has been cut through what was previously the stone retaining wall on the north side - and is continued by the new terrace right up to the National Gallery - the upshot is that Trafalgar Square has changed shape. It has become visually much longer in the north-south direction. It is less contained. The fountains and Nelson consequently feel weirdly as if they have been shoved further south.