They say that it always rains in England, that's not "entirely" true. It does rain a lot though. But London is very nice place to travel, even in Winter.There are many things you can do in London.
In London you can Ice-skate in many places. In Marble Arch, Somerset House and Natural History Museum, among other. Also London's landscape is really beautifull when snow sets in. So don't hesitate to travel to London even in the winter.