My BMW 328i M Sport was recently involved in a car accident where a pick up truck drove into the rear of my vehicle whilst I came to stop in traffic. Significant damage to the rear boot, lights and bumpers and chassis as well seems to have bent inwards. The other party's insurance claimed liability by the next day. The vehicle was recently assessed and it will cost about £8K to repair, by a BMW approved repair centre. The MV of my car is about £18-20K (Jul 2013 16K miles). However, I have a few concerns regarding the repair.

1) I'm worried that although the car will be repaired to manufacturer standards, it won't hold the same trade in value the car would have had before the accident? What % drop would I be looking at if I traded it in at a BMW garage itself?

2) Is there anything I can do in terms of the difference in diminished value? Can I claim that back from the other parties insurance? What options do I have?

3) I'm guessing I have no say in terms of I'd rather dispute it with the other party's insurance over getting a write off vs get it repaired?