Thank you flameport, so while it sounds like I could replace the flex outlet plate with a socket and call it job done, would it be remiss or out of the question to do so without changing the RCD type? Worrying, as that RCD type is being used throughout the house including for sockets.
The...
OK, so the house CU has a 63A 30mA RCCB, then a B20 MCB for the garage circuit. Then 2.5mm to the junction box, then 4mm from junction box to the garage main switch (Eaton Memera 2000) with 100A rating.
So, 12 year old house with dedicated circuit from CU to garage. This runs twin and earth to a junction box by back door, at this point the wire changes to 4mm, to the garage. The garage has a further mini CU with a lighting circuit and a circuit powering electric garage door and several sockets...