Flashing glow plug light loss of power?

hi i have 2004 2.0tdci ghia 5 door,
i start the car a mormal, wait for the glow plug to go out car starts up, the first time this happened i went about a mile and the glow plug started flashing and i had a loss of power, the second i had been driving for about 30 miles with 2 stops so engine was well warmed up, both times i pulled over turned the engine off and turned the ignition on wait for the plug to go out and i was on my way, this problem has happened twice in 10 days.
any ideas please.