The car is a Focus 2.0 TDCi with 153k miles. The engine takes a couple of attempts to start cold and hot. I can drive for 50 miles, stop to fill with diesel and the engine won't start first time.
If I give it 1/4 throttle as I start, it will usually start first time. The glow plugs have been fitted for about 120k miles so are probably past their best but given the problem happens when the engine is fully warm, I don't believe its the main problem.
I'm trying to figure out what the 1/4 throttle is doing to help.... is it giving extra fueling or is opening the throttle valve helping in some way. Once started, the engine performs just as good as it did when new.