Mike Halmarack ... wrote:
To lag these pipes properly would mean pulling up a lot of
floorboards.
Does there really need to be quite so many air bricks allowing such a
cold draught in a floor of this type, at this level?

It's a fine balance.
You really, really don't want to get rotted floors, due to condensation.

Water comes out of the ground as vapour - if the underfloor is not
properly sealed, and from the top, though the floor.
If it then condenses, when it hits the cold underfloor void, bad things
happen.
I wonder how much power heat recovering vent bricks would save...