So the sink has one of those smooth rounded-topped plugs that pops up and down into down the plughole.
When you push the plug down it sits in place, and you release it by pressing it GENTLY again - and it pops up again.
Someone didn't do it GENTLY and it is now stuck in the hole. There is no catch or lever to raise it so I assume there is a busted spring underneath!
It's quite snug in the hole so impossible to prize out. Its a pedestal sink so the base is enclosed.
Any ideas?