In reply to mypyrex:
A single feeder that doesn't include the return leg to the consumer unit required to make it into a ring circuit is known as a radial circuit (it is not a spur, which is a radial subcircuit off a ring or another radial circuit). Radial circuits are perfectly acceptable under bs7671.
However, a 2.5mm t&e radial circuit supplying sockets must be protected by a 20A (or lower) rcbo and since it is buried it must be enclosed in a suitable conduit or duct, and be at a sufficient depth to avoid being damaged by any reasonably foreseeable disturbance of the ground, and be marked by cable covers or marker tape.
It sounds like a DIY bodge and the earthing and bonding requirements are quite likely to be inadequate. More info is needed to determine exactly what the requirements are, such as supply arrangements (e.g. pme, tt etc.), presence of extraneous conductors, exposed conductive parts, garage construction etc..