If you go back into the main section of this forum, 'Clipping In', you will see events with the title 'An Introduction to Club Cycling' with the DATE. The next session, on 10 October, is currently full, but keep an eye out on the thread in case someone drops out. There is one each month.
As an alternative, you could come along to a Sunday morning C ride. These are very friendly and not vastly different from the Introduction Rides.
Group riding is not as daunting as you think ;-) We also run group-riding skills sessions - sadly you just missed one, which took place yesterday at Regent's Park.