I cut both the outer shells and the feed tube with pipe cutters, but I put a piece of wooden dowel wrapped in insulation tape to make it a snug fit inside the blue feed tube to stop it flexing while cutting.if you know a plumber or gas engineer copper pipe cutters are perfect for the job.Use them on the hard shell and then a decent hacksaw on the blue raceway.
http://www.plumbworld.co.uk/pipe-cutters-616-0000