I love London in November. Spent nearly the entire month there last year. The majority of it in London.
Recall one day of heavy rain, heavy enough for me to utter aloud, "maybe I should have packed the travel umbrella." However the torrents ceased by mid day and exploration continued. Also recall the Lords Mayor parade on the 4th that I was there to photograph was inundated with showers but went off without a hitch. This was a day after the horrific Paris Bombings. I expected to see stringent police activity during the parade. Saw little and had to be reminded by a local that London is always on alert since the days of the IRA but that doesn't mean they live in fear. Quite the opposite.
There were a couple other days of light sprinkles but nothing curtailed my enjoyment of the city. Did Experience a down pour during one of the days i was visiting Durham but that made it the perfect day to explore the stunning Cathedral.
All in all last November wasn't terribly cold either. Dressed comfortably in layers. Waterproof parka with lightweight Polartec beneath. Carried gloves but rarely wore them.
Christmas lights along Oxford and Regents streets and up and down side streets were lovely. Most pubs had Christmas trees. Selfridges and Liberty were in its full blown Christmas glory. Amazing stores!
The Winter Wonderland in Hyde Park was up and running. Its free and although I didn't think I'd like it, meandered about it around sunset one day and enjoyed watching the arcade and amusement rides light up. The food/beer hall was huge! There was also a haunted house with an exterior that looked like the result of a Game of Thrones battle scene and I remember thinking " Really? For Christmas?!!"
With the exception of one group of 20 school children and 10 other visitors (yes I counted them) I had Hampton Court to myself. Honestly, spent over three hours there. VERY enjoyable day out.
So yes its a good time to visit London. One of my favorite months to go and I've been doing such for a number of years. Feel free to PM for more London in November thoughts.
Enjoy your visit.