Any UK Caters out there can recomend (from experience) a good capo that can cope with the various string diamiters of a 12 string?

I play my 12 in open D, which is great for tunes, but way off my keys for singing to! Trouble is the capos I've tried out never hold down the octave strings properly - creating a gawd awful cacophony!

I'm on a fixed income so I can not afford to just buy-to-try, so if anyone knows of a capo out there that actually works well for what I need it to do I'd really appreciate a heads up on it (and maybe a url too?).

Thanks

Wrinkles