Hope you don't mind - I'll tell you anyway! There's a fuse in the plug!
Every socket outlet is fed by two 2.5mm sq twin and earth cables, one from each side. The cables are run in a ring which starts and ends at the circuit fuse in the consumer unit, and an (almost) unlimited number of sockets can be installed in the ring. The supply is fused at 32A. However - every plug contains its own cartridge fuse, which is sized appropriate to the appliance. Most common are 3A, 5A and 13A (which is the max). So every appliance can be appropriately fused. But every plug, and every socket, is the same size and shape, regardless of its load. The (then) 30A rating was chosen on the grounds that most people had a 2kW electric fire, a few had a 3kW fire, and some also had an electric kettle or toaster. At the time no-one had a dishwasher and few people had electric washing machines (!) but they were expected to become popular.
When I read the old Electrical books from 1946 I was really impressed at the thought that went into it (we had 6 years of total war, many homes destroyed by bombing, with no supplies of copper wire or electrical equipment available for housebuilding, and all the tradesmen drafted into the forces or working in munitions factories, so needed an entire rebuilding and renovation plan). So we were starting with a pretty clean sheet, and could standardise and supercede the many different sizes and shapes that had been designed by different manufacturers, or used for different purposes. As well as the ring main, and the standard fused plug, the square-pinned plug was introduced at the same time as it can be manufactured to give a more relable contact, resistant to wear; and the cable was put at right-angles to the pin axis to discourage people using the flexible cord to pull plugs out of their sockets. All plugs are earthed, and the earth pin is larger and longer than the others so that the earth connection will make first and break last. The socket is shuttered so that until an earth pin has entered, the phase and neutral orifices are blocked so a child can't poke a nail in and make contact with live parts. You can tell I think It's a terrific design.
The plug is rather over-engineered, and quite big, so when we go over to a single European standard it will become obsolete (I worked in the Distribution and Supply industry for some years, and one of the principles of the new European standard is that it shall be completely new, so that no one country has an advantage).