I have never done a group ride off the north american continent. If I end up vacationing in the London area what are some good, pretty fast rides I could do?

This is a pretty quiet forum, and I'm not going to be able to help you directly, but here's a couple of pointers that may be useful.

Richmond park is a pretty good cycling venue (to the annoyance of drivers)
https://www.londondynamo.co.uk/faq.php
https://www.timetriallingforum.co.uk/...showtopic=4606

Evans, a big chain of bike shops that is despised by cyclist, runs some rides
https://www.evanscycles.com/categorie...rganised-rides

hth