It is easy to misunderstand, we have in the UK a number of parallel systems:-
The radial as name implies the wires radiate out like tree branches.
The ring final the name final is important as it means the ring must never be broken, and there should be no circuits from it, however it is not quite true.
The spur is a twig off the main branch or ring final and relies on the fuse in plug to prevent over load, so can only supply one item, (socket double or single of fused connection unit [FCU]).
The fused spur, really a radial, because it has a fuse it can supply as many sockets as you want.
The ring final is nearly always 2.5 mm² (2.9 mm² = 7/0.029 in imperial) there is an option to use mineral cable but rarely seen in houses. Supplied from either 32 amp MCB/RCBO or 30 amp fuse.
The radial can be 2.5, 4, or 6 mm² and as a result can be supplied from 16, 20, 25, or 32 amp MCB/RCBO (15, 20, 25, or 30 amp fuse).
The British system allows many sockets to be supplied from one MCB/RCBO because it is normally 32 amp, where pre the 13 amp fused plug, the fuse board was full of fuses, there may have been two or three 15 amp sockets from the one 15 amp fuse, but with the fused plug common for 25 sockets off the one 32 amp MCB/RCBO.
However there are some draw backs, mainly down to maintenance, we should have an electrical installation condition report (EICR) every 10 years, less with rental properties, or change of occupant, which ever sooner, and this should high like loose wires and faults as the readings are compared with last one, so if last one shows 1.24 Ω and new one 1.34 Ω the inspector should look as to why, and any electrician should check on if the ring is complete before adding more sockets and after any work, etc.
However be it DIY or electricians being lazy, often the checks are not done, with a radial if a wire comes off the socket stops working, but with a ring final it will still work, so the user can be unaware of a fault. It is so easy for an electrician with his loop impedance meter to detect there is a fault, but for the DIY guy the loop impedance meter is rather expensive so he needs to open the consumer unit or fuse box to test, and that involves some danger, so often not inspected and tested after work is done, and for this reason some feel the ring final is not a good idea.
However on the plus side there are loads going for it, like reduced volt drop, but the DIY test plugs will not help testing a ring final as the first indication is around 1.9 Ω and the ring final fails at 1.4 Ω so you need not a £50 plug in tester but a £200 tester to ensure it's OK. But an electrician will have the meters required, so only problem is when DIY work has been done.
