If the rcd is tripping will all the appliances unplugged you may have a wiring fault. If the TD socket is getting hot or there is evidence of scorching around socket it could be a loose connection which is arching when under load.
You need an electrician to test the wiring and ensure its safe...
Have you tried switching off the supply to the garage it must be supplied from the house CU? I would use the switch on the garage CU to ensure no neutral path exists from the house.
DS
Mm, is that a fuse supplying that "spur"? Would that be a "fused spur" ? Oh, lets add a switch.
That would be a switched- fused- spur ideal if you don't want to use a "plug top" !:ROFLMAO:
DS