Considering it's an offence to allow the gas to vent into the atmosphere (leaks not being counted) it really needs to go to somewhere that have the equipment to collect whatever gas may still b in the system, pressure check it and if necessary, locate any leaks. Once any repairs if required have been completed they can then re-test the system then re-gas.
you are right... (I looked it up to be sure, - it seems strange that they sell kits for this potentially illegal activity in high street stores!)
perhaps i should clarify the advice I've given:
on searching for leaks, I said you may buy dye chemicals to find a leak, and you can buy freon detection devices to find the leak.
Adapters for recharge can tell you about the system pressure.
using those methods, you should be able to find the leak, and determine if the system is pressurized, if it is not pressurized, you won't be venting any gas as there is no gas in the system.
(the refrigerant UV dye packs do not contain refrigerant) - so you're not using refrigerant to find leaks.
https://ior.org.uk/app/images/pdf/C...on Commercial Refrigeration Systems 18.12.pdf
The section 2 of that doc covers
Specifically, it is an offence to put refrigerant into a system that is known to leak.
...
Every year I get my air con gassed up, every year it passes the vacuum test, and every year it's empty again after the winter.
So every year you intentionally put gas into a known leaky system?
You *can* do this at home (fix the air conditioning) (and you can do it legally too, but the tools are expensive, and the system may be dangerous to work with...)
You can take it to the same sort of place that RWB does, they will whack in a can and charge you £99, (and presumably say see you next year)
If your long term plan was re-gassing every year and ignoring the leak, it's illegal regardless of whether you take it somewhere to do that, or do it on your driveway.