In Ireland all the rooms came with a substantial hole in the wall, mandated in case you decided to put something like a kerosene heater in your room, although the heating was electical. I generally had to block them off to stop the wind whistling through.

That's more for ventilation to prevent damp etc (Ireland has humidity issues). Modern houses typically have MVHR instead.

Right - I think it was to handle Carbon monoxide (and general ventilation). If you look at part F here I think current regs are 6500 square mm for most rooms https://www.seai.ie/sites/default/files/publications/Domesti...

(TBF Irish standards have gotten much better for airtightness)