Please report dangerous drivers to the police - Roadsafe. Report to plod, not just whinge here.

Got a response from the company:

Thank you for bringing this to my attention. I have forwarded this to the relevant department heads and they will do a thorough investigation.
Kind regards
Catherine

Catherine Entwistle
Director

And here's my original message:

Forgive me if this is not your responsibility, but yours are the only email addresses listed on your website.

I am writing to flag the driving of one of your delivery drivers. I was cycling westward through the City at approximately 7.20am this morning (Leadenhall Street > Cornhill > Poultry > Cheapside > Newgate Street > Holborn Viaduct) and encountered one of your vans stopped at a red traffic light at the end of Cornhill by Bank. The van had crossed into the box for bicycles and there were bikes in front it. I pulled up alongside on the driver's side, but held back slightly. When the lights changed the driver accelerated aggressively, shouted from inside his cab, peeped his horn, and drove close behind the bicycle in front. He continued in a similarly aggressive manner along Poultry and Cheapside. I encountered him again at the traffic lights beside St Paul's, where he shouted abuse (directed at me, I think) when another cyclist crossed the red light, and from where he accelerated aggressively through traffic, cutting up a black Porsche, into Newgate Street. After this I did not see him. The van's numberplate was XXXXX.

I have reported this to the Metropolitan Police's RoadSafeLondon service. Driving in London is dangerous enough; there is no need for inconsiderate, aggressive drivers to make it more so. Hopefully you can impress upon your drivers the need for all road users to behave with care and consideration to others.

So...no idea what will happen, but hopefully some of these companies do take complaints of poor driving seriously.