Hi Garth,
Looking at a picture of the Sealey SuperMig 180 on their website it looks as if the welder wasnt originally fitted with a Euro Torch connection and was supplied with a Hobby Mig style permanent fit torch. That type of torch would have had a gas valve fitted within the torch behind the trigger.
Basically all you need to do is get a gas solenoid and connect it to the welder. If you have a search on the forum there will more than likely be a thread or guide on how to fit it, as each make of welder may differ.
I carried out the above conversion on my Kende 150R welder, and it took me 2 days to work out how to do it, but I managed in the end.
cheers
Gav