My wifes TD4 did the same to us 2 days ago. Driving for an hour on the highway, pulled over for a coffee & after 5 mins stoped (alarm not activated) the little oil burner turned over but no one home!
Rang local dealer for idea's & tried locking/unlocking etc, with no help. Couldn't hear fuel pump so swapped relays checked fuses & eventually pulled the "out" hose form the sensor/sender unit on top of tank off (thought that was the in tank pump - bad info from dealer!), after that it burst into life....
Read somewhere else last night it happens very intermittently & one guy had his TD4 with the dealer for 3 days with no joy!