Any petrol car that is compliant with Euro 4 and any diesel car that is compliant with Euro 6 is ULEZ compliant.
The big impact would be on diesel vehicles since due to the NOx emissions cap they need Euro 6 which isn’t only stricter but newer so older diesel cars aren’t compliant whilst pretty much every petrol car from 2007 or so would be.
So tradesmen vans and other work vehicles would likely to be severely impacted by this which will increase the prices to the end consumer since they’ll just roll over the daily ULEZ charge.
Your plumber isn’t going to buy a new van especially since the enlargement of ULEZ is going to crash its value they will however pass the ~£20 charge onto you the next time you call them like they already do with the inner London ULEZ.