ICC is not currently affiliated to any leagues, however, we are putting on our first road race in two weeks and will then be applying to become affiliated with the ERRL next year. As we are in North London we are in the Eastern region due to British Cycling choosing to split London between 3 regions so this league makes the most sense.
Currently crits are the best attended races and there will often be multiple ICC racers attending one race. There is a thread in the members only part of the forum that most members will try to keep up to date with the races they have entered. I imagine that if we become affiliated to the ERRL it will be more common for people to go to road races together as they can be far more confident of getting a place. We are still quite a young club and racing as a team is something we are looking to improve on.
On your separate note, normal Sunday rides will almost always be long enough to be outside the M25 for a significant period of the ride. It's also fairly common for people to suggest multi-modal rides involving a train journey and a ride. Bigger trips happen fairly often as well, ~10 times a year, from weekends away doing Way of the Roses to training camps in Gran Canaria. Often if something is suggested you will be able to find a couple of people who are interested!