Anyone needing a decent quality air con service in the Oxford area would do well to try
A.C.R.E..
My air con seemed to be getting noisy but still worked. I booked the car in at ACRE in Carterton where a leak-check, dye-test and refill was carried out for £48 all in. No leaks but the gas had run very low, and there was no service record of a previous fill.
In comparison, SAAB in Oxford wanted £120 for the same job (although that included cx'ing the pollen filter - a job I can do myself though I did get them to offer the job without the pollen filter for £65).
The work carried out at ACRE was in my opinion, pretty thorough and I have had no problems since.