They demanded that as part of the COVID bail out package for TfL then Tory candidates consistently slagged off Labour for doing it. It absolutely was party political.
This has been quoted often and it is false.
This misunderstanding (whether portrayed accidentally or deliberately) stems from a letter, dated 14th May 2020, from Grant Shapps, then Secretary of State for Transport, to TfL. It sets out conditions for the government’s Covid bail-out package to TfL:
The condition relating to ULEZ says this:
The immediate reintroduction of the London Congestion Charge, LEZ and ULEZ and urgently bring forward proposals to widen the scope and levels of these charges, in accordance with the relevant legal powers and decision-making processes.
At that time, the proposals in train to expand ULEZ and which TfL were being urged to bring forward, were to extend it from its initial boundary (which was the inner London Congestion Zone) to the North and South Circular Roads. It is this expansion which that letter refers to. Sadiq Khan's subsequent decision to expand ULEZ to the whole of Greater London (which is the plan that caused the most controversy and was said to have cost Labour the Uxbridge by-election, among other things) was not a requirement of the TfL deal. In fact, the government explicitly told the Mayor in the final settlement letter (30th August 2022) that he was not allowed to use the bailout money on the ULEZ expansion:
22. Road User Charging. You have decided to consult on proposals for the introduction of a London-wide Ultra Low Emission Zone for introduction in 2023, to improve air quality in London. TfL have estimated this will cost £250m in capital infrastructure costs. HMG grant funding in this settlement should not be used to cover the costs of your policy decisions to charge road users, and therefore if you choose to implement this scheme or other road user charging options, you must fund them through alternative sources available to you.
Finally, at Mayor’s Question Time on 21st July 2022, the Mayor was asked, categorically, who was the “decision maker” to expand the ULEZ zone to encompass the whole of Greater London. Page 26 of the transcript, here:
Neil Garratt AM: Thank you, Chair. For the proposal to expand the ULEZ to the whole of London, who is the decision maker to do that or not do that?
Sadiq Khan (Mayor of London): Me.
Neil Garratt AM: It is your decision whether that proceeds or not?
Sadiq Khan (Mayor of London): Yes.
It is wholly false to suggest that the TfL emergency funding package had, among its conditions, a stipulation to expand ULEZ to encompass all of the GLA area. The proposal already in train was the intermediate stage and the Shapps letter merely suggested it be brought forward. The final expansion, to the whole of London, may have been in the Mayor's mind at that time (I'm quite sure it was) but no proposals had been published and no conditions to implement it were imposed by the government as a part of any funding package. Not only was it not party political, it was not true at all.
Hopefully that puts that to bed.