So straddling both draughts and insulation we have wall vents.
Upon investigating why our house lost all heat almost as soon as I turned off the gas I found that all the wall vents were simply a piece of plastic on the inside and out with nothing in between.
In a best case scenario you might have some fancy passive vents but you always a pipe from the outside to in on a very slight angle.
In our case just a series of holes in the walls. The lack of a pipe meant that cold air had immediate access across every wall so you would get draughts even coming through plug holes.
Have still to resolve. Would appreciate any recommendations. Seems when it’s not done right the first time diy options are scare.