2007 Freelander 2 HSE

There were a few days where my car was cranking for a noticably longer time before firing, but I put that down to the cold weather (it was around -20C here in Northern Norway), and then the next day my wife drove the car to work and it would not fire up at all when she went to start it again at the end of the day, it just cranks endlessly.

The reading that will not clear on the diagnostic tablet was crash sensor? And one that caught my eye, but did clear was an immobiliser fault - which led to me changing the key fob battery, but that didn't work.

The little red alarm status light blinks once roughly every 5 seconds whether the key is on the ignition or the car is locked.

Does anybody have any idea how I can go about fixing this or where's a good place to start looking next?
Any help is appreciated