So there's nothing stopping the average Joe plugging 2 of these into a dbl socket that is connected to a 2.5mm 27A rated unfused spur and trying to draw up to 52A, and if unlucky enough to just draw 32A it won't trip the ring MCB but will overload the spur cable - and this is fully compliant. But you can't spur off 2 x 13A FCUs together which is max 26A and within the spur cables spec. Don't make a lot of sense.That's not the case, some are unfused and the regs say only ones with 3 or more sockets need to be fused (unless the regs have changed?)
Here just a couple of examples:
Adaptor
BS1363Multiple adaptor for plug socketsTurn a single socket into twoCompact cube shapeEasy grip designwww.toolstation.comMasterplug 13A 2 Way Unfused Socket Adaptor - White | Wickes.co.uk
Masterplug 13A 2 Way Unfused Socket Adaptor - Whitewww.wickes.co.uk