Actually J is not wrong, its 20 amp for a radial power circuit (a single cable feed to a point), and 30 amp for a ring circuit (a loop from the consumer unit to the points, returning to the consumer unit). If you’re having fuses blow for no apparent reason you should defiantly call in a qualified and NICEIC approved electrician. The fact that you have fuses at all suggests that your electrical system is rather dated and could probably do with upgrading. Fuses in new installations have now been replaced by miniature circuit breakers (MCB's) and have a slightly higher current rating than their equivalent fuse type. A ring circuit MCB would be rated at 32 amp.
Regards
MikeW
MikeW, March 2008