I found a "plus" for Homebase, for the first time in ages ...

Fitting IKEA smart lamps, I could use a B22-E14 adapter for the 600lm
bedside light, but did not have the space to use a B22-E27 adapter for
the 1000lm ceiling uplighter.

Looked for a replacement E27 pendant lampholder, TS/SF don't stock any
(despite selling E27 lamps) all the ones available online seem to be
ugly 1950's designs, and require 38mm shades instead of 25mm shades (you
can get 25mm-38mm adapter rings, but obviously not the other way round).

Then found these on the shelf in Homebase, they look normal, and fit
normal UK shades.

https://www.arlec.co.uk/product/cord-grip-lampholder-e27-long-skirt