water coming from back of loo?

Our bathroom was on an outside wall. An extention was added to that wall some years ago., so the bathroom wall now backs onto tv room. Just noticed carpet and skirting board soaking and moaldy! This happened a few years ago, and we thought it was the cistern overflow pipe ( which we don't think had been re-routed by builders.) Hubby chnaged ballcock level so water does not go down overflow anymore. Everything has been fine for past few years and we noticed this tonight. We have taken off bath panel to see if leak came from there and is flowing through outside wall ( unlikeley I know) Does anyone have any ideas of where it could be coming from?

Many Thanks