Hello and help ? TD5 Defender will not start

2003 Defender TD5
I left the keys in the ignition overnight (ignition off) and now my landy wont start.
All ignition lights come on and fuel pump runs but the engine will not turnover.
The immobiliser light is solid red (not blinking).
Interior lights that are activated by opening the driver's door have a slight flicker.
I have checked battery and earth connections. All look good
Had used low drive and diff lock yesterday - so diif lock light still coming up on dashboard.
Any clues ?

Have you tried locking and then unlocking?

As it sounds like it is immobilised.

Cheers

Hi Neilly - yes tried that and have done that method on previously owned 300 tdi Discovery - but not getting any bleeps at all when going thru the unlock process...?
seem to be in a strange state ??
Cheers

Have had this on a D2, seemed to have brain freeze, only way around it was to disconnect the battery for 15 minutes.

"Normally" on a D2 this is a case of the wrong fob, ( one not fitted with a passive immobiliser chipset in the fob, or the passive coil is fubarred). Thus locking then unlocking only, resets the passive immobiliser system and allows it to start, But as said this would be on a D2 , do not have any info for a Defender setup and how that works, sorry

Cheers

As mentioned by other contributors, try disconnecting the battery and waiting a few minutes. The radio coil for the transponder is around the ignition barrel on a TD5 Defender, make sure that the key fob (which contains the transponder) is waved close to the ignition barrel.

Thanks both - will try the battery option and get back to you !
Cheers

Thanks Neilly and MarkA-Lanark .... the battery approach has worked perfectly. Really appreciate the help.
After a few gear changes and a bit of reversing the Diff Lock light is now out ! (Normal Landrover !)
Cheers again for your speedy answers
Regards
Vince