On turning the ignition key my Fiesta will turn over a couple of times then shuts down. All the dash lights go out except the immobiliser indicator light. This will continue until the battery is dead, but if I use a boost pack it starts up !!!! Does this make sense and can anyone advise please. Cheers

 

dead battery's can do strange things to modern cars. have you tried a new battery?

 

Yes and after a while the problem returns.