https://www.lfgss.com/conversations/131099/
That’s an old archived thread from London Fixed Gear & SS Forum which got developed into a full on guide on what to do and they stripped out the anecdotal stuff and “best wishes” and stored it as a guide.
While it may be clear cut now, there’s a chance that the driver might suddenly change story when he finds out how much a new bike costs! A mate had this – driver offered to pay assuming I think that a bike was £200 at Halfords. When she discovered that the bike she’d just written off cost well over 20x that, she changed her story and it was only thanks to witnesses that it all worked out OK.
Joining BC now won’t help, you have to be a member at time of incident. However there are a number of decent cycling-specialist solicitors out there, check out Cycling UK or Cycling Weekly pages for links.
Get in touch with the witnesses and also report it to police. Go through insurance – that’s what they’re there for.