Andy Burns wrote:
Asking about something I've seen done, rather than something I'm
thinking of doing ...

Gas pipe enters building through cavity wall (it is sleeved) at a
height above ground floor ceiling and below first floor floorboards,
crosses room and descends to cooker. Should the floor/ceiling void
be ventilated?
Gas safe register tech bulletin #113 may have something to say on the
matter, but I can't find a copy online.

No, almost every house in the country has gas pipes under unventilated
floorboards, there is no requirements to knock bricks out of walls.

My gas meter is downstairs, my boiler is upstairs, as is every other house
on this estate, about 180 houses (meter at front, boiler at back).

None of them have vents at joist level and are not required to do so.