Personally speaking, I would give Halfords a wide berth myself.
There are a whole bunch of decent VW/Audi/Skoda specialists across the country that it would be difficult not to find one close enough by you to use, and are far less likely to rip you off (find extra work that needs doing with high markup for example) or miss things out. I am not saying that they are all bad, but I would prefer someone who looks after the particular marque who is likely to know the tricks and has the experience to get the job done quicker and more effectively.
I am sure someone will be along with recommendations if you let us know your approx location.
If you are in the South West I have personally used AudiVolks (Keynsham) and MCCM Garage (Midsomer Norton), both of which I would recommend, now I am back in a VAG I will certainly be using MCCM again as they are close to me and looked after my old S4 very well in the past.
I have also used MRC Tuning in the past and that knowledge of the specific brand (Audi in this case) meant he could do a very quick fix on a repair he found during the health check pre-mapping without dropping out subframes and replacing a relatively expensive part entirely.
