You don't need a licence to weigh scrap copper in, apart from a driving licence that is to get there that is. Make sure you sort it out first. Cut all your fitting out off the pipework and bag separably. This will be classed as brazerey (pardon the spelling). Next put all your pieces of copper with the fittings removed in a second bag, this is clean copper. If you have any brass fittings or taps ect, bag this in a third as this is classed as brass. As for your cylinder spend a bit of time on it and strip the connections out of it, remove coil (if has one). This way the cylinder is now classed as clean and you get more for it. Step four take it all down to your local scrappy. Ask about and see who pays the best, other plumbers normally know. Step five don't tell the misses how much you got, go down to the local boozer and enjoy.