Surely there has to be some sort of law/legislation that says "you did the work, car is no longer safe/fit for purpose". I dont have a clue about things like this, but have you tried Citizens advice? I would what that other guy said, give them a very detailed itemised bill/invoice, a report from progrip possibly backed up with pictures (possibly take your mates car in, and compare, take pictures) make a diary of everything that's happened, from moment engine went bang to now, support it with dated invoices and reports. Then, most importantly give them a diary of work carried out while it was inside progrip. Send them a tracked/signed for parcel, with all that in it, and a formal letter. Just tell them that you have been to another specialist, and they have proved that their is a fault with your car since the car went in for remedial work on xx/xx/xx. As the fault was with their workmanship, and they was unwilling to help, you are presenting them with a bill for the works carried out. Give them a date that you want the matter sorted by, telling then if its not sorted the matter will be taken further. if nothing is sorted by that date, then I THINK you have a case for the small claims court.
Ring CAB though, they will give you great help in this. Hope iv helped
as they drive them day in day out, they should be able to confirm quite quickly if there is an issue
