If it's leaking onto the floor then put down towels and call a plumber.
If it leaks only when you flush it call the plumber out during the week.
If it's leaking into the WC pan then there is no urgency. It probably needs an adjustment to the water level. You can do this yourself or have someone do it for you.
Take the lid off the cistern and watch the mechanism as you flush it. There's often a small nylon adjusting screw that sits on the float arm and sets the water level by turning off the inlet valve. Screw it in a few turns and do up the locking nut - or call a plumber to have him do it for you.
Peccavi, April 2011
