Carole, you'll see plenty of mentions on here of the Harrogate Crime Festival - in fact, the organizing team has also just joined Crimespace. It's held every July, is friendly, attracts a lot of the top authors and has rightly developed a reputation as THE crime event of the year in Britain. Nearly everyone who attends once goes back for more, and I think that's about as good a recommendation as you could have.
For something different, there's always the St Hilda's Crime and Mystery Weekend, held at St Hilda's College, Oxford, during August. It takes a more academic approach, with invited authors presenting papers on a specific topic, but is always friendly and good fun.
Wow! Thanks, Stephen! A friend of mine (not on this site) who writes said I should attend conferences. I thought to myself I'd be afraid to open my mouth, if I did go. But I'm going to go anyway. Bull by the horn type thing...! again, thanks!