See also these threads:

Ring circuits UK style.

Ring circuits revisited

Ring circuits? Spur unit? RCD Device?

This article (PDF) from the IEE journal:

Origin of the BS1363 plug & socket

The key point is that every BS1363 or fused spur connection to a ring should be protected by a fuse of no more than 13 amps.

The imported "wall warts" are just using molded BS1363 plugs in the cases and not providing the proper fusing which is part of the specification.

Quote
Are you sure there isn't a thermal fuse up against the primary winding under the first two layers of tape?


Yep. I stripped the outer layers back and the wires just go straight on to the primary winding.