Technically, the system is sealed, so it should never need re-gassing unless you have a hole in it etc.
Here's what I'd do.
Take to Kiwk Fit, ask them to re-gas.
They'll pressure test
Find that the system isn't sealed
Run dye through system to identify leak
HOPEFULLY the leak is in the condenser (AC radiator type thing).
Tell kiwkfit thanks, there will be no charge as they couldn't gas it, they'll offer to replace for £800 or something silly.
Contact cliospares, buy new condenser (if that is the issue).
Your system will be empty of gas, because the first thing Kiwk Fit do it drain the system, take the front bumper off, replace the condenser, take back to kiwk fit and they'll fill it up for £50.
Sorted.