TD5 Immobiliser problem after reconnecting battery.

Good point, I can't remember if the negative was disconnected and it wouldn't make any difference to the fix if the negative was disconnected, but as you say it is good practice to disconnect the negative before the positive terminal.

I've had a play around today now I have had the vehicle towed to a quieter location where I'm not going to **** off the neighbours.

With the key in the ignition and connecting the battery the alarm goes on for about 30 seconds after which it turns off. When turning the key dash lights come on and I can hear things priming but will not start. After it goes silent if I take the key back out and in again and turn I can hear things priming, no alarm but still won't start. The blue light is flashing as though the alarm is on though.

Looked through forums for various reset procedures but nothing works. I really don't think the fob I have is linked to this system.

Close to giving up and going for an expensive trip to the garage.