Thanks for the link cct. Given the comments and linked docs on the thread I was hoping to find one with a slightly lower alarm threshold than 30ppm. Put whilst I look for a better one, I think £15 to have one sitting on the passenger seat is very worthwhile.
A mate borrowed a plane from the same fleet I rent from a few years back to give his Dad a flight. His dad slept through the flight which he was a bit miffed at, then on short final for no reason he can recall he went around, finally landing (far from a greaser!) and starting to get a splitting headache. You've guessed it - cracked exhaust dumping CO in the cockpit. I think both him and his Dad used up one of their 9 lives that day.
I'd forgotten that story as it was before I started flying lessons, but it came back to me reading this thread, and now with a PPL of my own and having read everything here, it's time for me to take CO more seriously.
If anyone does have a link to a UK supplier of the CO Experts model, I'd still be interested to hear.