Overnight trips from London in December

There are LOTS of places to consider. These are ones I would think about if it were me: Cardiff- good shopping and a short train ride from London York- good shopping, good history, and again, short train ride from London Rome- I've always wanted to go there and imagine Christmas time would be very nice. Especially if you can get a cheap air fare. Salzburg- Love it in winter! Their Christmas market is one of the best in my opinion, but even after the holidays it should be nice. Vinenna- nice in winter- but would probably be better before Christmas- love the Christmas markets there. If you are wanting to celebrate New Years somewhere special, Edinbrugh would be great. They call it Hogmany(hog-mo-nay) and it is BIG. Might have troube getting reservations at this late date, though. You could also try Inverness or Glasgow.
What about Scandinavia? Oslo is lovely and you could maybe do the "Norway in a Nutshell" train ride. You might possibly get a chance at seeing the northen lights. Amsterdam is nice, but I haven't been there in winter. I can't really speak to Paris as we didn't like it the one time we visited, but others love it. Both it and Amsterdam can be reached by the Eurostar train from London.

We adore Paris during the Christmas season, and visit at that time almost every year. The city is ablaze with lights, and there are amazing Christmas markets - featuring plentiful mulled wine! - with excellent people watching and delicious food. There's ice skating at rinks around the city, carousels set up for the kiddies, pretty flocked trees on many corners, and the decor at the grands magasins is over-the-top in the best possible way - it's FABulous!!! Copenhagen is delightful at Christmas, too! The Danes just have a flair for cozy and inviting and festive - and Tivoli is sooooooooo charming at that time of year. Strasbourg is another city that's lovely during the holidays. They have a wonderful German-style Christmas market (Christkindelsmarik?) that's stuffed with oodles of wonderful goodies and terrific decorations. I love Edinburgh and plan to go there for Hogmanay one day, but as Toni cogently notes, it might be a little late to get reservations. Rome would be great. I've only been in Rome in the summer, and would have enjoyed it far more if the heat hadn't been so oppressive and scorching. And I will just bet that there is a lot of excellent Christmas hoopla and decorations, especially around St. Peter's and Vatican City.

I would stay fairly close to London in either Amsterdam or Paris, both of which I like. Have been to Amsterdam multiple times, including a December visit which in 2010 had vicious arctic winds and snow, ( required silk longjohns, sweater, vest and down coat layers) but the city is compact so walking or taking the tram was still easy. Great museums and decent food there along with the interesting architecture; I suppose better food in Paris, with the possible exception of rijstaffel which I love. Have been to Paris several times but only as late as October, which was cool enough for thin blood.