HELP . Weird starter problem on MK2 Desparate !!

Hi all .
         I have the weirdest problem . The other night at 2 am , the neighbours found my Granada 2.8 mk2 running on the path !! They could not contact me but after 40 minutes it stopped . The car had not been touched for 2 days . When I came to it , the battery was flat so I charged it . As soon as I connected the leads , the starter turned and the engine fired !  In the end I removed the push on connector from the solenoid . After a while I returned to the car , put it in Park and reconnected the solenoid . Everything then went back to normal . The car now starts and runs normally . I can find no issues with any of the electrics and I have never had any problems before . How on earth can it suddenly without any warning , start up like that . I know there is an ignition take off lead from the solenoid so I realise that once the solenoid becomes live , the engine can start , regardless of the ignition switch . What I don't understand is how it happened in the first place . I have no idea where to look and I am scared of leaving the car anywhere without removing a battery lead !
               HELP: PLEASE ?

Well from what you are saying about the battery being flat might mean it is draining somewhere and shorting out, highly likely something to do with the starting circuit. Have you tried a "shoogle" test? Shaking the wiring in and around those areas and see if it tries to start?

Very strange that it is managing to short and start. I would be starting with the ignition switch. failing that call the exorcist!