Architecture: What will Jeffrey Archer say?

On Saturday, Will Alsop went down to the Thames waterfront at Gabriel's Wharf to paint on canvas - live - his thoughts about the future Mayor of London's home and assembly. This week, his colourful sploshes have landed him the commission to design the interiors for one of seven real-life locations shortlisted for development by the Minister for London.

Blackfriars Developments were so impressed by his concept that they fired the architects who had already begun the interior re-fit, in order to get Alsop inside their listed building. Their choice for the new Mansion House, Victoria House in Bloomsbury which was built in 1924, is strongly tipped to be the future Mayor's home. From its WC1 postcode alone, Victoria House is easily the best location on the shortlist.

Two exhibitions, hanging side by side at the capital's Oxo Tower Gallery, illustrate the cross-fertilisation of ideas for a new building to house the Greater London Authority. "Masterclass 98" features six canvases from six architects - Will Alsop, Edward Cullinnan, Piers Gough, Eva Jiricna, Jeremy Dixon and Edward Jones and Tony Fretton - who were given just six hours to come up with ideas for the Greater London Authority Building.

In an adjacent gallery is an exhibition of seven locations for the future Mayor of London's HQ, shortlisted by the Minister for London, Nick Raynsford. The developers of the sites have presented their ideas for the building to canvas Londoners' opinions. In six weeks' time, the Minister will announce a shortlist of two or three for the next round.

Never mind who is going to be mayor of London. Where he, or she, will be based with 25 members of the Assembly looks like being an even more controversial question. London may be a cultural trailblazer, bursting with new ideas and youthful icons of art, pop, fashion, food and film, but the Mayor's headquarters has to send out the right message about governance of the capital. All eyes are off the Dome for the moment, and expectations are focused on the Ministry for London to find a home for the new Mayor and Assembly that not only reflects the spirit of the times, but creates a coherent civic identity.

The assembly building must be accessible and easily reached by public transport, as well as not being seen to be off-putting. It must unite north and south London as well as east and west. Worse, it has to be procured on leasehold for just 15 years, which means that the Government has to work with property developers to find the right site.

When Donald Dewar, the Minister for Scotland, had to find a location for the Scottish Parliament, he involved architects. At first he commissioned feasibility studies on Edinburgh locations and then, at the last minute, found an entirely new location in Edinburgh before putting out on open competition the brief to design the new Parliament.

Nick Raynsford has no wish to get into that sort of architectural jump- off for a leasehold building. There is no shortage of potentially prestigious buildings, thanks to corporate belt tightening - the empty Shell HQ is on a prime riverfront site - but this made his task more difficult, owing to the cultural baggage that accompanies a civic centre for the Mayor.

As the client in a real estate deal, the Minister went to estate agents Knight, Frank & Rutley and got them to sleuth six locations, tactfully dotted along both sides of the Thames from Vauxhall to London's docklands. They are at Canary Wharf, E14; London Bridge City Road, SE1; Regent's Place, Euston Road, NW1; Vauxhall Cross, SE11; Wilton Road, SW1; all of which require new buildings on site, and also Camelford House, SE11; and Victoria House, Bloomsbury Square, WC1, both existing buildings that require refurbishment.

Camelford House is to get a sail in the foyer and some potted plants; Victoria House was going to get a Sixties-type conversion to the blandly lit, homogenous anonymity that passes for good design in the US - until Blackfriars Developments saw the light and got Will Alsop on board.

New buildings proposed for the four other sites by the developers are not much better. What sort of Mayor would move into the shimmering, Saatchi- style gloss and glamour of a new glass building by Munkenbeck and Marshall near Victoria Station?

It's handsome, but it doesn't send out the right vibes. Terry Farrell's new building proposal for Canary Wharf is in an unusually sober and restrained mood - as befits the pomp and circumstance of the Mayoral office - which is a shame, because that is one of the few sites that matches Farrell's exuberance.

Foster Associates' new building for London Bridge City Road was knocked off in such a hurry that they show, in section, two completely different versions of the same building - one with a curved stern and prow, the other with the stern straightened. The Regents Park project has a nicely rounded glass house by Shepherd Robson, nestling into view from the Euston road.

More imaginative ideas, but bound to get the controversy going, are hanging in "Masterclass 98". Apart from showing what good sports they are, Piers Gough, Edward Cullinan, Jeremy Dixon with Edward Jones, Tony Fretton, Eva Jiricna and Will Alsop prove that you do need an architectural debate to find out how local government should be seen to be done.

Jeremy Dixon and Ed Jones junked the hypothetical site at Gabriel's Wharf proposed by the organisers, Architecture Today, to build an hierarchical tower block jutting into the Thames at Hungerford Bridge. Tony Fretton left the canvas blank, in a very conceptual, Jay Jopling White Cube manner, as a background to computer-aided designs and some exquisite white paper models of his low-lying transparent riverfront building, which allows passers-by on a public footpath to glimpse Ken Livingstone frying his fish, or tending to them.

Residents mix with politicians. Mayoral life is a beach in Piers Gough's ice-cream cone, painted purple, with photovoltaic cells to store sunlight dripping from its south-facing side. Typically, the building hides function in fun packaging. The assembly is stored in the base of the inverted cone while the public are let loose on the Thamesside beach created by the building.

Gough brought his own gold paint to give it a little glitter. Edward Cullinan went for the big statement with an hierarchical tower that places the mayor's overnight accommodation below the penthouse suite, where the public gallery has the best views across London. Will Alsop gave the mayor something to think about with a garden of contemplation "in the vain hope that wise decisions will be made" atop an invitingly open and layered building, rather like a club sandwich, with the politicians in the middle fed by the administrators and informed by the public.

Eva Jiricna's exercise in narcissism involved covering her canvas with reflective silver foil, collaged with black-and-white photographs of lips and faces. It's her in-your-face way of confronting us with her notion that the Mayor doesn't need a building at all: "In fact it would be harmful to the democratic process." Democracy in the digital age means screens to mirror on-line what happens on street corners and inside assembly rooms. To her, the idea of a special landmark building for the mayor is as dead as the gold chain which comes with the office. In this, she may be closer to Nick Raynsford's thinking than she realises.

As the Minister for London himself says: "Nothing is writ in stone. At this stage we are searching for the site and identifying the best one, and using both exhibitions for a cross-fertilisation of ideas. There are ways in which we can get what we want. I haven't ruled out changing the key players on any one of the chosen sites." But will the property developers listen to this?

"Oh yes, I think so." Nick Raynsford openly marked Will Alsop's card: "He did le Grande Bleue for local administration in Marseilles, and has a very strong track record of public buildings."

In Marseilles, the city council and regional government officials love going to work in an egg painted bright blue by Alsop, and not least because it is ecologically sound.

So a makeover by Alsop of staid old Victoria House, built 74 years ago with a rather hierarchical occupation - "even certain lavatories may only used by certain people" - looks like being the winner. Watch this space.