Slow down you're gonna crash

So, a couple of weeks ago there’s a squeal and a bang outside the house as a twunt drives into the back of Boy’s car when he came home for lunch. No injuries thankfully, and only minor damage. Independent witness standing by, and bloke accepts liability (“Why did you stop?” “Because I live here” “Sorry, the sun was in my eyes”) and I get all the details and photograph the 57' skidmark and start dealing with insurance. The garage estimate is a touch under £800 as long as nothing goes wrong; the car’s not dangerous – the main problem is that the tailgate doesn’t shut securely so the back panel needs pulling out, and possibly a new tailgate. Parts are cheap* – labour and VAT are expensive. I refuse to allow them to say the car’s not worth that much and write it off, because they wouldn’t give us enough money to buy a suitable replacement. We’re still waiting to see what the various insurance companies decide as to who’ll pay what, but if they won’t play ball we’ll have to cancel the claim and try to come to an arrangement with the other driver to get repairs done ourselves. Surely they can't force us to hand the car over if we don't want to? Surely the other guy's insurance must cover the repairs?

*comparatively speaking.