hard to start and engine cuts out

I've got a Skoda Octavia 1.9tdi (2008). In the morning when the engine is cold it takes a good 30 seconds to turn over and start it, when it's started it goes fine.On a longer trip on the motorway it lost all power and stopped, I pulled over to the hard shoulder and whilst still free wheeling bump started it , then it happened again and again, but when eventually running with reduced power, trying to accelerate it juddered violently. Took it to our garage who could not find any relevant faults. No warning lights came up on the dash. Its very intermittent because the next day it runs ok