Well it is all done and dusted and I now have a fully working freezing air con, topped up with anti bacterial treatment for £32.95
Yes it was just a plug it in for an hour (no leak detected, and as we know the machine will not fill up with gas if there is a leak ) scenario but that is all I wanted and expected. I knew the system had a leak in it, in fact it only had 20g in it, but it is a slow leak as the last top up was over two years ago. The operative was not conversant with air con even to the point that he did not know that a leak sealer is available, it is just another job for them.
Anyway I can keep cool for another two years for a nominal fee and will investigate Larry's suggestion for the leak