Thanks all.
I've bought a couple of expanding rubber plugs (quick cam-lever operation) to block these holes, and the electric bilge pump will take care of any excessive water ingress (from rain, etc), and then my intention is to get a small manual bilge pump and mount it on the transom, with the pick-up pipe sitting in one of these little 'wells'.
The electric bilge pump will take care of any large amounts of water, and the manual one will quickly get rid of the remaining inch or so that the leccy one won't pick up.
The purpose of these holes remains a mystery, tho', as we bought the boat new and it never had anything in there - they are simply open drain holes!
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