Just back from London. You definitely do not want to

bring the heavy bulky stroller. During rush hours, you won't even be able to get to the tube with all those people walking through the small corridors and passways. Even at non-rush hours, it is very inconvenient because many tube stations have stairs in narrow passways. You need two people to lift the stroller up and down often. In London, the key is light weight and small space occupation.