Where does the OP live, if in London I want to come over and see this badboy in person.. I'll get my face in the paper, become famous and rich beyond my wildest dreams 🙂 mwah ha ha haaaaaaaa
Seriously though, allanwhyte77, where are you based? If the water has been properly isolated and the cistern is dry and you've emptied the pan it's pretty miraculous that water is still leaking into the pan.
Disconnect the water inlet pipe (while still isolated) and see if that's letting by. I would normally assume the siphon (flush valve) to be the culprit but if the cistern is dry then *shrugs shoulders* something strange is happening at the ranch.