Those who think tradespeople should not have to pay Ulez/CC (or that Ulez/CC should be scrapped to ensure that no tradesperson has to pay it), should anyone belonging to a trade also get free public transport when they are using that? Because to be logical and consistent, that's what you'd have to do.
Come to think of it, why stop there? Perhaps anyone belonging to something defined as a trade should be allowed to fill up a trolley from the supermarket for free, get a free house from the government, free flights to go on holiday...
Controversial opinion: People who work as builders or plumbers are not actually better or worse than people who work in other jobs. They are not some kind of salt-of-the-earth bollocks, they are not providing services as a charity. They are just people doing a job. And it is OK to ask people doing a job, any job, to please pay for the things they use. That includes road space, which is a limited commodity. Or public transport if they are using that.
Society should do things to make sure that people who work in trades can do their jobs comfortably, safely and easily (and one of the THE most important things they can do in that regard, BTW, is to limit congestion and parking pressure so that tradespeople do not spend half their lives stuck in traffic jams). Society is not, however, under any obligation to give tradespeople stuff (such as modes of travel) for free which other working people are not getting for free.