Excellent info, Charnwood, thanks!
Am in N.Cornwall. Plumbase in Bodmin so will try there.
EDIT**So, if I've got this correct in my head :idea:, if I buy: 2 x Philmac 9133 couplers
1 x Philmac 1332 adapter
and a piece of 22mm copper tube. I should have everything I need to...