It's going to cost an extra £30-£50 to test it and if it fails you'll get it back with a big hole drilled in it by the tester.
£100 would be ok if it had between 3-5 years of test left, you could always try diving or air gun magazines. They usually have classifieds at the back or at least web sites where you can buy/sell.
That's what I was thinking £100 is a bit much for an un tested one.
Found this is one on an Airgun site
However they are blooming expensive new,got to factor in postage as well ,I've got two 232 ones to sell may put them on e bay first.