Seems you have an internal overflow fitted to your cistern, your ballcock needs a new washer fitted, whats happening is your cistern is over filling, the excess water is just running down the toilet through the internal overflow, this is wasting many gallons of water every day, ask your landlord to get a plummer in to fix it a.s.a.p. its a small job. Good luck.
Freddy Fix it., March 2006