Involve the police. Most perps are gambling that their victim can’t be arsed to chase it up with the police, and later via the courts…
Remember that idiot who rear-ended me a year ago?
His insurance firm told me to get a convicition to get past the “waiver” they wanted me to sign, which would have meant I had no comeback if I had done.
I refused, duly pressed charges, got the conviction, and eventually, - a grand out of the insurer. If they’d offered me half that within a week of the impact - I would have gladly taken it.
Idiots and crooks all - insurers and their best customers - the “high premium” drivers that line their pockets with premiums more than you can buy a decent second hand car for! 
Refusing to give details, leaving the scene of the RTC, and driving his own vehicle in an unroadworthy condition were the charges on my perp’s sheet…
He got fined just under a grand, and got 6 points - PLUS his insurance company won’t pay out for the damage to his own car, because I had to submit to police that I believed the guy was over the limit - enough for his own insurers to seize upon, and invalidate his own prior fully-comp cover with them. His car was worth £12,000. Mine? - Less than a grand.
If the perp’s yard refuses to cooperate - then a soliciter’s letter threatening legal action possibly involving a winding up order will ensue - once a conviction has been achieved vs their driver whom they breached their own duties (to the public) in protecting instead… The winding up order scares small outfits, whereas the threat of a lengthy court case with massive amounts of evidence presented by yourself (along with expense claims!) tends to scare even the big boys…
Everyone tries it on these days. No one wants to just go “Bosh. A fair settlement right away sir - here you go.”. More’s the pity. 
Make 'em pay for their lack of vision. 
I didn’t have to attend court, and I didn’t have to fill out much in the way of forms. It was just the damned waiting and waiting that drove me up the wall for what I figured would be an “open and shut” case in my instance. You’ve got pics. That’s good if the guy’s got form especially. If a court case ensues, you’d be surprised at how much his firm will back down - rather than risk perjuring themeslves in court by being asked awkward questions… Indeed, “Mr Bloggs Is No Longer With The Company” is the obvious knee-jerk reaction by the firm - not good if one is the idiot trying to get the firm to back you up over being got bang to rights by our hero losing a mirror here… 
