I love the cheek of the Tories with this ULEZ thing.
Mayor Khan and all local government authorities are mere creatures of statute. They can do nothing without parliamentary authority. They have no independent power whatsoever and if they exceed their powers the courts can and do slap them down for acting ultra vires.
In this case, the legislation behind ULEZ was passed in this Parliament, which the Tories control.
They could, if they wished, repeal the legislation or heavily amend it. They could, for example, make it so that ULEZ could only be implemented if conditions A, B and C were applied. They could even require a local referendum.
They don't because it's politically useful to blame Labour for these schemes, and they know that the electorate will often be taken in when they, as Tories, in effect oppose their own freaking legislation!