Conservative members of the London Assembly have complained that Norman Foster's City Hall building is "falling apart". Ken Livingstone says they can move out.
They also complain that the flooding activated the building's emergency system which opens all ventilation shafts, causing rain water to come through the ceiling.
Conservative members claim that Norman Foster designed building has been beset by problems since it opened in July 2002, including internal windows spontaneously cracking.
"Much like his administration, Livingstone's building seems to be falling apart around him," says Angie Bray, deputy leader of the London Assembly Conservatives.
"If this is the standard of architecture he normally commissions then Londoners should be very worried."
However, City Hall was commissioned by central government before Ken Livingstone was elected in 2000.
Mr Livingstone's response is predictably robust. He told 24dash.com: "As the Tories on the Assembly have such a low opinion of City Hall, I would be more than happy to move the Tories out of the building and make alternative office space available for them elsewhere.
"This would free up much of the sixth floor they currently occupy for people who would do a more productive and useful job for London."