Got a 4 way block with a 2m lead, from by box of electrical bits, to test my newly arrived bandsaw. Plugged it in and "pop", everything in the workshop went off. unplugged the extension and tried another one. Every thing OK.
When I opened up the 4 way block I found THIS.

What is worse, this is on the back.
How do they get away with putting a BS number on stuff like this?