The Tories say the recent spell of hot weather is proving too much for City Hall - dubbed 'Ken Livingstone's Castle' by the opposition - and it is now 'falling apart'.
The Conservative Group in the assembly has claimed in a statement that temperatures in the building last week topped 28 degrees centigrade and that it had to be evacuated twice because of flooding on the lower ground floor.
Staff have complained of unbearably high temperatures caused by ineffective air conditioning and rainwater leaking through ceilings, it continues.
The Conservative Group, which occupies the sixth floor, says City Hall has been plagued by problems since it opened in July 2002.
However, Angie Bray, Deputy Leader of the London Assembly Conservatives, scuppered the party's line of attack by suggesting Ken Livingstone was personally responsible for commissioning City Hall. In fact it was ordered by central government before Livingstone was elected in 2000.
She said: 'Much like his administration, Livingstone's building seems to be falling apart around him.
'If this is the standard of architecture he normally commissions then Londoners should be very worried.'
In a typically outspoken retort Livingstone said he would be 'more than happy' to move the Conservatives out of City Hall and free up space for people who 'do a more productive and useful job for London'.