So probably a company DIYer or even a qualified engineer did this!
It does almost look as if somebody may have just bought a reel of Arctic flex and fitted a plug and trailing socket, leaving it coiled up on the original drum.
Assuming this was fitted with normal BS1363 connectors, the highest-rated appliance one would expect to have been connected would have been about 3kW, drawing around 12.5 amps on our 240V supplies.
Of course, if somebody had shoved an adapter or power strip on this extension and then connected multiple loads, the current could have been more. The 13A cartridge fuses in our plugs will carry a substantial overcurrent for quite a long time.
