Nathan Critchlow-Watton wrote in message
Just to make it clear, the air vents are plasterboarded over, so
wouldn't vent smoke directly from the room - although I've no idea why
else they would be there!

The plasterboard is presumably a relatively recent addition.

Either way, blocking it up for a while seems a good idea.

So is there anything stopping the rain blowing against the PB from outside?