I did my 2nd intro ride with the Manchester Wheelers yesterday. I can highly recommend going along to one to check it out. The pace on these rides is kept at 15mph and they try to keep everyone together, but do wait at the top of hills or at junctions if anyone drops off the back.
Prior to the 1st club ride I went to, I had done a 30 miler at about 16mph but found maintaining 15mph in a group FAR easier, I was worried about not keeping up but I shouldn't have been
- As long as you are reasonably fit and can happily go for a few hours on the bike, you should be fine on an intro ride.
They're very sociable and you can chat all the way round to get a feel for how the club is. I'm joining the club this week - I have found riding in a group to be ace
List of rides here
http://www.manchesterwheelers.co.uk/rides/list.htm - You can just turn up at the intro rides.