I hate to bring the bad news to you, but the same went on mine and cost 500 quid to repair. It is part of the cats which need to be replaced because they are obviously part of the flexi. I was thinking something around 50 quid to have a new one welded on, but apparantly (and i took it to a few places) you wouldnt be able to. You may be able to find one from an alfa breakers, but in the end i couldnt find one so gave up and bought a new one from alfa. (which was also discounted at that price!!!).
Short term fix though, there is a piece of aluminium bar i dont know what it does because it just ends suddenly above the flexi, but if you bend that to push the 1 section of the exhaust tighter against the flexi, it will stop the gas escaping.
I dont know if that made sense^.