As The Boy says Oxford and Bristol are probably the best two on the market for Distance Learning. I did mine at Bristol and found them very good.
However which ever school you finally choose, don`t under-estimate the sheer volume of work involved and the amount of time it will take.
If you are able why not visit the two schools and see which one is right for you. If you go during the last two weeks of the month there should also be students there on Brush-up courses who you can ask questions of.
DWW