Vauxhall Corsa exhaust back box welded - need to seperate???

Hi,having purchased a new one I need to get the old back box off, and the previous owner or garage have welded the back box to the mid-section. I have managed to get the clamp off but just can not think of how to break the weld. I may be able to get hold of some cutting/burning equipment from my brother, but have to wait till he can get it from work. Does anybody have any other bright ideas in the meantime??? really do not want to cut it, as then it will be shorter and pose more problems. Anything posted will be greatly appreciated.