Thanks for tip! Have booked in with them tomorrow morning. Looks like check is free and gas for my model is £50.It probably needs the gas topping up. I think Halfords will check it out, but not charge if they don't get it working better (confirm before letting them loose on it)!
Defo sounds like a bodge job should have gone on a machine for about a hour.So they didn't plug it into a proper air con machine, vacuum test for leaks, then refill the system?
Hope it keeps working for you, but bear in mind all aircon systems start to leak eventually, so it will need looking at again sometime in the future (hopefully a few years)!