Have a look here, a decent club will let you attend a couple of sessions before you join to get a feel for the quality, level and type of people, but bear in mind there are dicks in every club and sometimes the ones who are most willing to be friendly are the biggest dicks!
http://www.britishtriathlon.org/clubs/index.php?club_name=®ion=5
Have a look here, a decent club will let you attend a couple of sessions before you join to get a feel for the quality, level and type of people, but bear in mind there are dicks in every club and sometimes the ones who are most willing to be friendly are the biggest dicks!