Scott wrote:
Why are there several ways to wire a lighting circuit when there is
only one way to wire a ring main?

Because usually things on a ring circuit don't have remote switches. If
all your lights have built in switches, there's only one way to wire a
lighting circuit. If all the sockets on your ring have separate
switches, they can be wired the same two (or three really) ways. But
lights normally have separate switches, and sockets normally don't.

A simpler version is that there's four ways to wire a switch to a
switched load:
1) The switch is built in to the end accessory.
2) "Junction box" wiring - the "main line" of the power circuit connects
to a junction box. Live goes to the switch, switched live comes back,
switched live and neutral go to the load.
3) "loop in" wiring" - the main line of the power circuit goes to the
load (light) which has an extra terminal - effectively a built-in
junction box. Live goes to the switch and switched live comes back.
4) I don't think this one has an official name - the main line of the
power circuit goes to the switch. Switched live and neutral go to the
load.

Note that two or more of these - even all four - can be mixed on a
single circuit. None are more correct than the others but some are more
common. Lighting circuits usually use 2 or 3, sometimes 4. Power
circuits use 1, though 4 is used in kitchens (where there's a switch
above the worktop and a socket below).

Mike