I had no issues riding around in London, there are bike lanes in certain areas but you can get away with riding on the roads or the footpaths. Traffic is always congested and slow, for the most part. You can take bikes on trains during certain times of day but only when the train is above ground. Check TFL, they have a journey planner for people who wish to take bikes.
Plenty of spots to ride too, there is a group on facebook if you are looking for people to ride with.
https://www.facebook.com/groups/691675010843613/
Lastly Finsbury Park is awesome, definetely worth checking out.