It sounds like your situation is ideal for a drop bar road/gravel/cx bike, especially if you're planning to do longer rides or with a group.

Never been to London, but I hear it's wet, so you'll want something that can accommodate fenders, and disc brakes as well. They stop better in the wet. All the big name brands have some version of a road bike with these features. Some will be able to accommodate wider tires if you plan to take it on more mixed surface trails.

I'd say visit your LBS and see what's available there. They can help you with the fit as well as future support and maintenance.