ignition problem

Help. I seem to keep getting problems with my TD5 nobody around here has come across.
Occassionally (3 times in 6weeks) I jump in the car, turn the key and although the engine turns over it shows no sign of starting. If I then relock the car with the key fob, unlock likewise, put the key in the ignition, low and behold away we go. I thought it was the immobiliser playing up but apparantly that even prevents the engine turning over.
Anybody come across this before?

when it does it does fuel pump run with ignition on

Put a new fuel pump relay, just to rule this out... R1 in engine bay fusebox

Hi. Yes the fuel pump does seem to be running

Hi, Many thanks that is now on my to do list.