EGR and DPF do not prevent particulate emissions. They just reduce them. If yours isn't Euro 6 then your particulate emissions are too high.
It wouldn't, because the particulate and NOx standards are different between petrol and diesel cars.
No, these have to comply to the same standards, and the TfL bus fleet will increasingly be full-electric.
What figures, can you provide a reputable reference? (For the record, the right wing Press, i.e. the Mail/Express/Scum/Torygraph/GB News or similar is not "reputable"; a source like TfL would do).
Compliant petrol cars are very cheap. Euro 4 petrol, which is the standard, became mandatory from 2005. Any non compliant petrol car is seventeen years old - hardly anything of that age bar classics is still on the road, and as classics are really just for occasional use you'll just pay the charge for those. £500 will probably buy you a compliant small petrol car, or certainly £1000.