They claim that the £18.5 million spent by Livingstone's Greater London Authority in the year to the end of August 2003 was not about providing Londoners with impartial information but to achieve positive PR for him in advance of next year's mayoral election.
The figure means that the GLA's annual adspend is now in line with major advertisers such as the furniture retailer MFI and NatWest.
GLA's initiatives include a £5 million campaign through TBWA\London to sell congestion charges to Londoners.
It also splashed out almost £5 million, according to figures from Nielsen Media Research, on a TV, press and poster initiative produced by M&C Saatchi to boost the number of people using London Underground services outside the daily rush hour.
Simon Hughes, who will challenge Livingstone for the Liberal Democrats in the next election, compared the GLA's adspend to that of the Government in the run-up to the 2001 general election.
Steve Norris, the Tory candidate, described the figures as "typical Livingstone".
He added: "Rather than spend vast sums plastering his face all over London, it might be better to sort out the serious problems affecting the capital like crime and transport."
However, the GLA insisted the figures were inaccurate and that most of its spend had gone on public information activity for Transport for London.
It claimed it had spent only £105,000 on advertisting in the current financial year.