In article , "Dave Plowman (News)"
wrote:

7/029". But TW&E in this size was in rubber before PVC, and then for a
few years before metrication. Which I can't remember when exactly, but
about '70.

Sounds about right. Our current house was built about 1968 using
imperial PVC cable. We bought it in 1970 and my earliest extensions to
the ring main were with 7/029 but 2.5mm^2 came in shortly afterwards.

Remembering to re-use the old BA size screws when fitting a new switch
or socket to an existing old imperial box has always been a pain.

--
Mike Clarke