So you've got a problem with either the clutch maker or the workshop. I dont really understand how a clutch can be a "head ache" so since that sounds strange to me, first guess is its more likely to be the workshop than the clutch maker. So, I would;
1. Find a new workshop. Ask them if there's anything else they typically do when replacing the clutch. It's common to resurface the flywheel, and replace the rear main seal and spigot bearing when doing the clutch, so if they say they typically do that, its a good sign.
2. Give them the history, then ask them to pull out the current clutch and look for any issues with the installation, or the clutch itself, then call you with what they find.
3. Expect to be buying a new clutch. If you go with what the workshop sell, then you have a one stop shop if there's any problems. Any time you buy a part from one place and have it fitted by another, you risk ending up in the situation you're in now, where they blame each other.
I can't conceieve of any reason that the clutch would behave differently with different weather conditions.