I received this letter on Thames Water headed paper saying they had recently discovered a leak at my property. It offers to send out a plumber for free to fix the leak. There is no leak at my property that I know of. The email address given is for a company called 'Essential Water Services Ltd' and the phone number given goes straight to voicemail. Does Thames Water outsource this kind of thing to third parties? Or is this some kind of misplaced/fraudulent attempt to drum up business for an independent company?