Since my original post I think I might be barking up the wrong tree with this. I have read more than once that unless the inside engine temp is less than 5 degrees the glow plugs wont kick in anyway.

Leak off tubes leaking perhaps?? Euro car parts do a set for less than £4 so must be worth a punt.

If this is an Hdi engine it doesn't need the glow plugs to start - unless you live in Sibera. It could be that the engine is not turning over fast enough due to a duff battery or starter.

Not common rail or hdi on these,but electronic pump.

Even so they're still direct injection, and should not need glow plugs for cold starting. In fact they don't even switch on for preheating unless the outside air is less than 2 degrees celcius. Their primary purpose is for noise and emission reduction during cold running.