My son went with his mates last September to Italy. They went to Rome for a couple of days, they were nearby, not touring. There are pictures of him in The Colliseum, St Peters Square, The Vatican, all over and it is empty. It could not have been better from a tourist perspective. Sounds very similar to your experience today. A great time to visit London, as you suggest.Just walked from Pimlico to Leicester Square rather than get the tube, amazed that the city is still so quiet, walked along the embankment through Parliament square, Horseguards Road and parade ground then through Trafalger sq. it’s an absolute pleasure to do. Honestly if you ever thought about visiting London but were put off by the crowds, do it now before the hordes return.