However, I can only see 5 wires going into the consumer unit - I would
have thought there'd be 9, assuming that both sockets and lighting were
on ring mains?

Firstly, lighting circuits are almost never run in rings, but in radials.
Radial circuits are ones that run in a tree like fashion, branching wherever
is convenient. (They don't have to branch, if they don't want to).

Socket circuits can be run in rings OR radials. However, standard 2.5mm
cable is not suitable for running a 32A socket circuit in a radial. Thicker
cable must be used (usually 4mm or 6mm, depending on details) or the circuit
derated to 20A.

I suspect that either your house is wired using radial circuits, or that
extra cables enter the consumer unit concealed from behind.

Taking off the fronts of sockets these appear to be correctly
connected on a ring main.

It is not possible to determine if a radial or ring circuit is in use simply
by examining the connections at the sockets.

Or is it possible for example for only the 'live' ends of the ring
to go to the consumer unit, with the other 'earth' end of the ring
being connected to the main supply (where I can't see it)?

This doesn't make sense at all. I do hope you aren't planning to do any
wiring.

Christian.