I work next door to a repair shop and they told me that the big insurers who have a list of nominated/approved repairers give them a fixed fee for each car (something like £1,700.00)
regardless of the amount of damage
So, you can imagine if they were to receive £1,700.00 for this job then they'll be rubbing their hands. You don't have to use the appointed repairers you know but you are encouraged too (for the reason above, so they know what the bill would be). I'd speak to the claims dept. and state that you wish to take the car to a repair shop of your own choice. It's no big deal as you can still drive around in it.
On a similar note, this guy had an Audi TT in which had been 'fixed' by fixed-fee's-r-us but the punter was unhappy with the finish.......turns out it should have had a replacement roof skin but they just filled and pulled it to shape......the true cost of the repair was closer to £10K by the time it was finished
That panel of yours will never look straight imo and Silver is especially difficult to do well.