I plan to redirect our ground floor front room next year.

Currently, the walls are unplastered, and we've rewired so floorboards
are loose, so any option is possible at this point.

My question is what, if anything to do about draughts from under the
floor.

We live at a T junction, with a road running off our road straight in
front of our house. This road is a bit of a wind tunnel, and the room
we plan to decorate gets the brunt of it.

The house is Victorian, and slightly raised with large cavities under
the floor-boards. There is also a metal decorated air-grill at the
front of our house which ventilates the space under this room.

Net result is that it is seriously cold and draughty at the moment,
and I can feel quite strong cold draughts if I put my hands over the
floorboard gaps in this room.

When we've decorated the room, I plan to get an underlayed berber
style carpet, which should prevent the draughts, but I'd like it to be
as cosy as possible for my children.

Is there anything else I can do to improve insulation/carpet warmth?

I presume blocking up the air vent completely would be a bad thing? Is
it worthwhile attempting any other sort of under-floor insulation?

Thanks for your input.