Keeping out the draft
Many older homes (still) have existing old fashion floorboards over the void: causing draft and dust because these boards do not have a 'modern' Tongue and Groove' construction. Gaps between the boards cause draft and dust coming through.
Knowing that exposing wood will add to the value of your home, it would be a shame to cover this old floor covering with carpets to make your home look and feel warmer. If needed new floorboards with T&G and at least 18mm thick can take the place of your existing floorboards.
If that is too much work and hassle you can quite easily install new (thinner) floorboards on top of your existing drafty floorboards to stop the draft and dust devaluing your home.
Plus in all circumstances it will reduce your heating bills!
(Filling the gaps between existing old floorboards is a very temporary - and 'ugly' - solution: due to the natural movement of the wood any filling material will drop into the void underneath the boards within a matter of weeks!
And no matter what you do: DON'T block any ventilation - air-bricks - in walls, your house needs ventilation to remove excess humidity. Blocking air-gaps can cause damp and the rotting of joists.)