即將離任的委員會主席Caroline Pidgeon指責市長堅持 "激進 "的項目時間表，"鑑於聯合街臨時住所的成功，這對我們來說似乎沒有必要"。
Sadiq Khan had claimed the move would save £61m over the next five years, but the GLA's Oversight Committee found the true figure was closer to £37m.
However, the Oversight Committee found St Martin's Property Group had been working with the GLA on a reduced rental offer which would have saved £24m over five years.
The remaining savings will be made from the elimination of rental costs and a reduction in energy costs at the Crystal, which was commissioned to be one of the most environmentally sustainable offices in the world.
Caroline Pidgeon, the outgoing chair of the committee, accused the mayor of sticking to an "aggressive" timescale for the project, "which appeared unwarranted to us, given the success of the temporary accommodation at Union Street".
She said: "Now we have taken residence in the new building, we need to get on with the job of holding the mayor to account and all these issues need to be transparently addressed.
"We look forward to the mayor's response to our questions and recommendations on the relocation of the home of London's government."
"The relocation of City Hall is saving £61m over five years to invest in London's recovery from the pandemic and protect vital services including policing, the London Fire Brigade and the transport network.