A compass works because one end is attracted to the (magnetic) North pole, the other to the South pole. So, a compass can be used to find either of the poles. But because the earth's magnetic poles are well below ground level, a compass becomes less useful near to them, the needle does not remain horizontal, but dips down towards the ground. In fact, because the lines of magnetic force are not horizontal, a good compass is be optimised for the latitude where it will be used. When exactly over the magnetic pole, the lines of magnetism will be vertical and so will not swing the needle one way or the other, it will just drift about. So the answer to your question is that a compass that is accurate in the UK is almost uselsss in Anarctica.