My wife and I spent Xmas and New Years in London a couple of years ago and loved it. We spent 10 nights at the Park Lane Marriott starting on 12/23. On 12/24 we went to Borough Market and assembled an in room picnic for the following day when everything was closed. There was no problem finding a restaurant open for the evening of 12/25...most hotel restaurants are serving. We also had no trouble finding theatre to attend during that period. Also, everyone should experience walking through Harrods on 12/24 (maybe just once though).