It was refreshing to see the London mayoral debate, chaired by Simon Jenkins, taking place at the riba last week: the institute as venue for a real public interest event, and in advance of almost everyone else. The candidates were surprisingly direct in their answers, and we scarcely noticed the absence of Frank Dobson (represented by the able Trevor Phillips) and Glenda Jackson. Ken Livingstone was on good form; Jeffrey Archer had done formidable homework (demolishing the theory behind congestion charging, for example); LibDem Susan Kramer was impressive and Darren Johnson, while having no chance, is likely to become a member of the Greater London Authority, given proportional representation. Not all the answers were accurate, however. Ken Livingstone thinks the mayor will be responsible for approving and implementing 150 projects a year in the capital. In fact the mayor will have no power to approve anything, but will have a blocking power - which can be overturned by the secretary of state. Jeffrey Archer thinks £7.5 million in rent for the Foster headquarters building is excessive. In fact it is a loss leader for the developers, who will get their money back from the increasing value of their office scheme which forms part of the overall site. Trevor came unstuck when appearing to support the idea of tied cottages for public-sector workers, but backtracked in perfect, New Labour mode. The institute's London Region should do more of this sort of thing. How about some public crits?