KKen what you have there is not legal you can not run a garage installation off of ring final circuit spur.
On what grounds do you claim it's not legal? It's not compliant with BS7671 but BS7671 is NOT law.
Part P (which hadn't come into force when this work was done) only requires "Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.". IMO provided the Zs is in spec and the cable is at least 2.5mm^2 this installation does meet that.
The poster originally wrote that the installation is spured off the ring final circuit. If he had said that it was spured into a FUSED spur unit then, it may be a little different. Though still not Ideal at leat the 2.5mm cable coming of the ring would have the protection of either a 13amp or 5amp cartridge fuse on the load side of the spur. Agreed that even the garage installation is pretty safe but you could argue that the 2 double sockets going back to the FCU is bad practice and wrong, they should be in parallel after the FCU. I just think that you should advise someone on the best way of doing the installation
If it's a direct spur of the ring then according to the 7671 it is not permitted. Again we can all argue that the 7671 is not a statutory document, but it can be used in a court of law, so to me if you do any work that complies it is legal. Would a sparks really spur off a ring to feed a small CU that will then feed more circuits, we just would not do it surely.
Again agree you can fit or install outside the regs provided you can prove that it is safe, but do you want to spend weeks in a court if anything went wrong trying to persuade someone what you did was safe, I wouldn't.
Think bottom line to work too is, any installation that exists and can be argued safe or not is pretty sound. Shouldn't we also be working to the standard of "Would I admit that was one of my installations".
If you look at something and you think I would not put my name to that, and when someone asks you your opinion, wouldn't it be right to advise a better way to do it. It is then upto them if they want to change it.
But arguing the semantics of wether it is legal, not legal, not this or not that, the final argument should be is it correct and the best way to do it. Doing it as the poster described is not IMO the best way.