Anti-start/theft system

[ColinCranwell]

I have a 1996 1.9 Diesel Executive.
It ran smoothly on Saturday.

Sunday; Try to start as normal, put key code in and get both the Red and the Green lights on the key pad saying light. The Red should go out and only the Green should be on.
The engine throws over but there is obviously no fuel getting through, which is what is supposed to happen when the system is not de-activated. Both lights remain on after the key is removed and go off after several minutes.
The little red flashing light on the dash, the anti-theft system armed light, is not flashing but on steadily.

I have tried leaving it for an hour but the fault re-occurs.
I have tried leaving it for an hour without the battery but the fault re-occurs.

Any ideas how/what to check?

Thanks.

Regards,
Colin.