They're like that in this apartment we're renting and I keep seeing them elsewhere. I don't get it.
at least in part it's an end result of decades of crud and tech debt, so to speak, accumulating in british power grid and home wiring. they do it this way because otherwise it won't be safe. continental euro home wiring usually has thicker wires, residual-current circuit breakers and no ring circuits so we get away without fuzes and switches, and with smaller plugs that don't become caltrops. sometimes we do have ring circuits kind of thing, but not in house wiring, instead it's in medium voltage distribution grid, and it's sized so that it can serve most of loads after single failure.
explanation
in normal state, medium voltage line (like 15kV, 20kV) might branch out in rural terrain from substation to two or more places. in case of single failure, mildly common after storms, everything downstream would be down. instead, to increase reliability, every few km there's a radio-controlled switch and some of the far ends have line between them that is usually disconnected. in case of single failure, damaged segment is cut off, and the far end of the loop switch gets closed. this way power is delivered the long way around the loop, allowing for repairs of the damaged sector in the meantime. this also specifically avoids some of problems of ring circuits especially in situation when some lines might be damaged.