My Fabia 3 was reversed into, and needs repairing - new bonnet,  light clusters etc. The 3rd party insurers have accepted liability. I can choose where I take my car to be repaired, the accident management company's preferred one being Alton Cars Ltd at Barnsley. They are Skoda approved, so have to follow the Skoda rules, and having popped in there, seem to to repair just about any make out there. Anyone had any experience/s of using them?  Alternatively, would I be better off having the work carried out at a Skoda approved main dealer bodyshop, ie JCT600, Vertu (VW/Skoda/Seat/Audi)? Has anyone got any experience/s of using any of these, or anywhere else in the Sheffield/Chesterfield areas?

No experience with Alton Cars but I wouldn’t recommend JCT at hillsborough. Like you I assumed a Vw approved bodyshop would do a top job but I had to take my golf back 4 times before it was right, and it was only a small ding on the front passenger door. The paint kept sinking and showing sanding marks/ sign of the original damage - although the colour match was good. 

I had a repair to my Fabia a few years ago.  I took it to a well known Skoda dealer in the North West but they subbed the work out to a bodyshop repair company.  like matthall94, I had to take it back a couple of times as I was not satisfied with the quality of the work.  So don't assume a Skoda dealer will do a quality job or any of the actual work themselves.