squiffything

Andy the guilt of theft is clearly weighing on their minds. Accepting their offer is for them a very cheap get out. No bad publicity the parts kept by them and sold on and most importantly no criminal record. For any business in the position they are in they should pay through the nose for what has been done to you. I would expect them to replace the missing parts fix the bike up for you (it is mainly cosmetic after all) and pay you the £1,200 as an apology.

Otherwise it's down the station of plod for you to do your civil duty and protect other innocent Law abiding citizens.