It gets weirder ! ! !
So yesterday, I jump start the car again, leave it ticking over for 30 minutes, then blast it down the dual carriageway for 30 minutes. Last night it started first time, this morning it starts first time. The only thing different is we disconnected a usb lead that has been there for 2 years, but then the car hasn't been left for 3 weeks before, so the next query is, can a usb lead that's not connected to any devices, drain a 12v battery in 3 weeks?? Or drain it low enough not to start??