Oi mechanic type folk! Rich Skuse, James Klos and anyone else with a clue.
The battery in the mother-in-laws K12 Micra went flat (don't know why), so I took the battery out and fully charged it, battery came back mint, I've put the battery back in, now the immobiliser cuts in and the car won't start. It's a keyless entry and ignition one, apparently a bit of a shit.
Does the key need re-pairing to the car?