In reply to joanneml:
Joanne,
Big Rock is super-friendly, so you will not have a problem finding a group just by introducing yourself. However, not everyone feels comfortable doing that, so here are some ideas:
You already know about their social climbing session, where an instructor will ensure you have someone to climb with, and will make you feel welcome. The instructors there are all absolutly fab, and really good at getting nervous or new people to feel at ease.
There is also a women's climbing session (I think Wednesday evenings), and just before that is a family climbing session (in case you have one of those).
You will also find the Milton Keynes Mountaineering Club are a friendly bunch who meet regularly, as well as doing regular outdoor trips.
http://www.mkmountaineering.org/
Why not book onto one of their lead courses? I find many of the groups who learn together then continue to climb together for years afterwards.
And of course, feel free to PM me as I climb there and have many friends there also, and will be pleased to climb with you/introduce you!
I don't work at BR, by the way, but do love it!