Heritage tours on London's popular Routemaster buses have been criticised for missing out some of the city's best-known landmarks.
The buses are being replaced after 50 years on London's roads
Tours should start by December when the last of the old "hop-on, hop-off" buses are replaced by more modern buses.
But London Lib Dems describe the proposed routes as "defective" for missing out such sights as Big Ben, the British Museum and Buckingham Palace.
Transport for London (TfL) says the routes are proposals at this stage.
Routemaster buses have been ferrying people around London for more than 50 years, but are being replaced on standard bus routes. TfL says they need to use more modern buses with access for disabled people.
More than 100 made their final journeys in September 2004 and now serve just five routes.
But they became such a London icon that some of the buses, dating from 1959 to 1965, have been refurbished to be run as a special heritage service.
Liberal Democrats on the London Assembly say two routes currently proposed, from Piccadilly Circus to Tower Hill and from the Royal Albert Hall to Aldwych, miss out too many sights.
Their transport spokesman Geoff Pope added: "It is simply staggering that the routes put forward by Transport for London ignore the most obvious tourist attractions in the capital.
"After all, Parliament, Buckingham Palace and Westminster Abbey would be on any tourist's list".
A TfL spokesman said: "There has been no final decision reached on the routes.
"We are more than happy for them to give feedback. This is part of the major consultation process we follow when we are looking at new or revised bus services.
"There will be further opportunity for consultation as and when the contract is eventually awarded to operate the routes."