Assuming the LABC give consent under Part P then yes. However at some point the SWA will need changing to flex with a box of some type. I know that RCD FCU is more expensive than plug in RCD but terminating SWA into a metal box will be required anyway so why not have the RCD FCU in that same box.
Screwfix price between £24.65 and £31.29 for RCD FCU and around £8 for plug-in type. To be to use plug-in is spoiling job for just a few quid.
If you think Part P registration is not required if you plug in then sorry you are wrong. If fixed in any way then needs Part P. So if you use an extension lead in kitchen and decided to nail in a few cable clips to tidy it up in theory you would need to register it under Part P.
So does not matter if you plug in or do proper job if you don't pay council their absorbent fee your breaking the law. So may as well do proper job.
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