OP
Deleted member 9648
Under the Electricity safety, quality and continuity regulations 2002 you cannot use a suppliers earth to an out building, on a TNC-S Earthing arrangement, so the detached garage effectively becomes a TT installation with an earth electrode installed in the ground.
If you use SWA to supply the garage the armour must not be terminated at the garage end of the cable.
God 'elp us.....what it it with outbuildings that promps otherwise competant electricians to spout complete nonsense?