Immobiliser active - after low battery problem

[GraceCourt]

Some months ago on holiday, my wife couldn't get our Galaxy Ghia 1997cc TDi started, however our breakdown assistance jump-started it OK... seemed strange but sh*t happens.  However, on Thursday it happened again... jump-started it OK again and I put the battery on charge for all of the obvious reasons... seemed to charge from partly-discharged to fully-charged as expected.

But the next day, "Immobiliser active" is showing when trying to start with both original keys, and the starter won't turn, not even with booster cables connected from another car to assist (and keep the voltage up).  Strangely, none of the internal lights now work (puddle lights are fine) and front ciggy-lighter is also u/s (it was fine prior to this) but all of the relevant fuses are fine. My usual (non-Ford dealer) garage recommended that it goes to a Ford dealer for full diagnostic check, but looking at previous posts there seem to be a number of Mk3 Galaxies showing strange behaviour caused by immobiliser faults. 

I'm going to have the car taken to the Ford dealer by my breakdown assistance and let them run the diagnostic check for Ã,£85 to see what they say but any comments/hints would be welcomed.

[GraceCourt]

Oops... sorry, omitted exact vehicle details. Mine is a Mk2 (2009 plate).