Tailgating

I have put my hazard warning lights on before now.

I'd let the Council know. It's dangerous for other drivers and for children on the bus.

There was nowhere to pullover on this stretch sadly...i will report to the bus company....though I doubt they give a shit

nothing to do with dvla.
would have to report to police; but unprovable, so no point.
just try to pull in/over if poss, to get out of harms way.
dash cams back and front is a good investment.

Ha ha Sodapop, you beat me to it. Safe distance is rarely
honoured especially around 12 o clock. I try not to be on the
road then.
I frequently slow down to make the point.

Way of life here in France my husband hates it.

It infuriates me to the point of precisely as M0nica has said, slow down, RIGHT DOWN....

No i have never reported anyone. Its idiotic driving, as you say, if you had to do an emergency stop it would result in the car that is almost in your boot, literally in your boot.

Ragtime
If you want to complain you might try your local council, they are the body that hire the bus.
Or, you could go straight to the bus company. Complaints of any driving transgression is taken very seriously.

My reaction to tailgating is to take my foot off the pedal and let my car slow down to walking speed. and then accelerate away. The vehicle behind usually gets the message and backs off.

But I agree it is a dangerous habit, but my feeling is there is less of it about than their used to be.