I have recently purchased a 1999 T reg 3.0 Stype. The rear door, drivers side, will not lock ,either remotely or manually. I cannot push the black loking lever in.  Can anyone suggest a solution please. 

It sounds as though the door latch mechanism has developed a fault (quite common on these models).

The good news is....if the door is unlocked and can be opened then it is an easy replacement job.

A new unit would be required if you cannot free the other one up by applying WD40 through the latch aperture.

Let us know how you get on with it

Thanks for your interest Trevor. I have now sprayed everywhere I can access in and around the door latch with WD40.As yet it has not resolved the issue. I wiil keep you posted.

Had a similar problem on my s-type when i bought it (had been in storage for over a year), lazy solenoid was diagnosed, but before replacing, was suggested to disconnect battery overnight ( with car unlocked :) ). Connected up following morning locked and then deadlocked car, unlocked, locked did this a couple of times, not had the problem since. Might be worth a try.

Thanks for the replies, WD 40 proved to be a temporary solution but then unfortunately the rear door lock changed it's mind and instead of being open all the time it became locked all the time. The result was that I took the car to a local independant body shop who managed to remove the door trim and open the door (I didnt ask how ) and replaced the complete door lock,cables,inner handle and latch plate with genuine parts  at a sensible price.All works perfectly now.