Brian Reay wrote:

As far as I can tell, there is no real standard for this stuff-

BS 4607 (has several parts) is the relevant standard, covering both
light and heavy gauge non-metallic conduits. Mind you a quick look on
the BS online web site shows this as flagged for obsolescence - to be
replaced by a harmonised BS EN, presumably.

As to manufacturers, Egatube (MK), Mita and Marshall Tufflex are the
names that come to mind.

--
Andy