Sorry, I didn't spot the previous mention of the Rogers Cadet. Other options for a cheap taste of valves might be an old valve receiver - Dave at Green Home Electronics has just sold two Sansui models (one of those was £125).

You could try http://www.hifiworks.co.uk/index.htm. He's in Cornwall, not too far from Bristol. I don't know anything about him, I've only ever looked at his website, but at the moment it's showing some good cheap stuff like a Scott Stereomaster, A Chapman pre/power and a restored pair of Heathkit MA12 monoblocks, none of which, I'd turn my nose up at.