Although you can still sell the cartridges and pump etc, i recomend you take off all non crucial parts(grips and anything else that can be removed, but not the cylinder[the bit that holds the cartridges].) as someone may want these for spares.
Other than that i suggest you take an angle grider to it or your looking at 5 years in the nick.
Edit:just saw your last post: you cannot sell them to ANYONE, regardless of whether they have a license, as of May you cannot buy, sell, be given etc and you have to send to a special place to be repaired if that is needed. You can only hope your local cop shop is understanding, as technicaly they cant accept it and are well within their rihts to arrest you if you try to hand this in and there isnt an arms ammnesty on. Hope this helps.