When left for more then roughly 8 hours (usually over night) and when it's cold, the engine will turn over for a good 20 seconds before slowly picking up speed and finally starting with a giant cloud of smoke. I think it's either:

a. Glow plugs

b. Injectors

or c. the fuel system (maybe pump or air in system)

Any takers on the most likely cause?.... Before I go and blow money on things that don't need to be done!