Donwill wrote:
I'm not sure what it's called but I will try and describe it's
description & function .

A standard approx 85mm square white plastic surround, to screw into a
standard wall box.
Has a 3 position switch, centre off, momentary action, what I would
call "press to make, release to break".
Press up to make a contact, press down to make another contact.
(change over) Spring release to centre off position.
Or possibly two buttons mechanicaly connected.
This is required to manualy open and close a motorised vent.

It's difficult to search without a name for this type of switch.
Cheers
Don
Many thanks for all the info, you can always rely on good old uk.d-i-y.
Have now ordered from TLC.
Cheers
Don