In itself, the Blue Carpet is nothing much. It’s relatively small, it cost a mere £1.4m, it makes a nicer place out of what was a grim nexus of roads in front of the Laing art gallery, part of the city where Georgian elegance meets 1970s tat and, generally, loses. Heatherwick himself tends to point out that the biggest single contribution to his square (actually it is a very irregular polyhedron in shape) consists of the mature trees - the largest ever imported into the UK - strategically placed to screen the roaring buses of the nearby streets.

The citizens of Newcastle, one gathers, were expecting something spectacular and concept-artish and globally significant - and instead got something subtle, right down to the inlaid brass strips dividing and edging the blue-paved areas. It’s an intelligent, quirky, upmarket little regional pedestrianisation scheme, that’s all. Hence the sense of slightly baffled deflation on Tyneside that greeted its launch. When something has been in the making for so long - getting well overhyped in the process - the final unveiling was bound to teeter on the edge of bathos. The sudden blizzard which turned the blue square white at the moment of opening was an appropriately surreal commentary on the whole business.

But it is interesting for other reasons. One is that it is the largest single thing so far designed by Heatherwick - one of our best and least categorisable young designers, first spotted at the Royal College of Art by Sir Terence Conran. Heatherwick, now in his early thirties, is equally at home designing furniture, sculpture, exhibitions, and buildings - anything three-dimensional. He has designed an all-glass arched bridge just for the hell of it - it may find a home in London’s Paddington Basin development - and has designed a church in Hereford and a temple in Japan. His forte is thinking things through from scratch, rather than merely putting a slick gloss on what already exists.

This attitude can prove difficult to the point of exhaustion. For a Glasgow design exhibition in 1999, Heatherwick made the entire display out of 60 miles of industrial cling-film. The amount of hands-on effort involved was almost painful to behold. Similarly the public spiral staircase in the Newcastle scheme was most effortfully made by a firm of Jarrow boatbuilders to produce a conker-like smooth glossy finish to its laminated timber structure. The downside to this is the cheap tattiness of the metal stairs themselves, which are already showing signs of distress. One wonders just how many of the 100,000 people who hit the city centre bars and clubs every weekend are going to notice either way - the good or the bad. If you’ve ever experienced Newcastle on a Saturday night, you’ll know that public-realm design niceties are not high on anyone’s agenda then. But cities are about more than Saturday night.