Heritage Routemaster bus tours have been criticised for missing some of London's most famous landmarks.
The buses are being replaced after 50 years on London's roads
The two routes, announced by Transport for London (TfL) on Friday, go from Trafalgar Square to Tower Hill and from the Royal Albert Hall to Aldwych.
But the Lib Dems described them as "defective" for missing sights such as Big Ben and Buckingham Palace.
TfL said the routes shadow existing ones, to allow for disabled access, and take in a number of attractions.
But the Lib Dems London Assembly transport spokesman Geoff Pope said: "It is simply staggering that the routes put forward by TfL ignore the most obvious tourist attractions in the capital.
Start from November
They cost £1.20 and accept travel cards
They will run from 0930 to 1830
Five Routemasters will run on each route
About 50 drivers and conductors in total will be employed by the operators First Group and Stagecoach
"After all, Parliament, Buckingham Palace and Westminster Abbey would be on any tourist's list."
But Mike Weston, TfL's operations director for London buses, told BBC News: "We are striving for a completely accessible network by the end of the year, which we are on target to achieve.
"The Heritage routes have to parallel existing routes for us to maintain a network that is accessible to the disabled.
"There are so many landmarks in London it would be almost impossible to take them all in but the routes we have chosen, after a six week consultation, take in sights such as Tower Bridge and St Paul's."
The last "hop-on, hop-off" Routemaster is expected to leave front-line service by the end of the year as TfL says they need to use more modern buses with access for disabled people.