I visited London a year or so ago for the first time in 30 years (and it was in November) and seeing the major sights wasn't a real problem. First night was the Hilton, Park Lane which made it an easy trip for Buck House and the Mall plus some of the main shopping streets. The rest of the time we were based at the hotel at Victoria station which meant one hop on the tube took you to Westminster from where it was easy access for Parliament, the London Eye, Tower Bridge, the Tower, and the Tate Modern (also HMS Belfast moored on the Thames) and St. Paul's. Like New York, a lot of the must sees were relatively close together. I stayed in Clinton and I only made two sub-way journeys, one to Brooklyn and one to 81st street and walked to and from most other areas.
So, if you are O.K. with walking about NYC then London isn't a problem.