The Spurs cutters are absolutely brilliant and are available from Harold Hayles, The Quay, Yarmouth, Isle of Wight, PO41 0RS. Tel: 01983 760373 or at www.spurscutters.co.uk. Possibly also at Halyard, but I don't know this for certain.
I chose them because the RNLI were using them at the time (may still be) and they are made in America. Don't have a big thing for the Yanks, but they are so litigeous, that I figured they'd over engineer the things just so they wouldn't get sued!!
First time out after fitting, it chopped through my mooring riser (25mm nylon) as if it wasn't there, and has dealt with everything else over a period of about 14 years superbly.