Cuprager wrote:

I know that you are not supposed to take more than one socket off a ring
as a spur but have never figured out why! Can anyone enlighten me?

For "spur" read "unfused spur." There's no limit if it's a fused spur
of up to 13 A (subject of course to consideration of the load likely to
be connected).

Unfused spurs are restricted to one single or double socket (or one item
of fixed equipment) because:

a) the rating of 2.5 mm^2 cable is assumed to be 20 A, but the circuit's
overcurrent protective device is 30 or 32 A, so does not provide
overload protection to the spur. Spurs rely on the plug or fused
connection unit fuse(s) to protect the cable. It's assumed that the
load on a double socket is unlikely in practice to exceed 20 A[*], but
with two singles there's much more risk of 26 amps worth of load being
connected, which could overload the cable;

b) even if you used 4 mm^2 cable to overcome the first objection it's
undesirable to connect a large load at one point on the ring (especially
a point near to one end. The ring circuit works on the principle that
the load is will be reasonably evenly distributed along its length.
Ignoring that principle greatly increases the risk of cable overload
occurring.
[*] Beware of the risk of violating this in the context of kitchen &
laundry appliances.

--
Andy