Computer science is a safe career choice - there is a severe lack of decent computing skills in the work force at the minute.
Computer Science, Maths and Physics are all very logical and have a lot of overlap. My advice is always to avoid specialising as much as possible unless completely necessary. Do the degree that you wouldn't mind spending the next 3/4 years doing, every day, all year.
Look at universities that incorporate different parts of each into their degree. On some courses there are a lot of applied mathematical modules which are almost verging on theoretical physics, similarly with computer science modules.
Honestly I would say do Maths but that's only because it is sort of an umbrella over them all and a good mathematician will almost definitely make a good computer scientist and physicist but I don't think it occurs as often the other way round. (In addition to me being slightly biased)