Change the diesel filter, sounds like its clogged. Mine did that when a crappy italian filter disintigrated! If you let it idle for a couple of minutes before trying to drive off you'll probubly find it runs fairly, this is bacause as the fuel is circulated it quickly heats up a bit which then goes through the filter better - enableing it to do max load. A new filter is always the first point of call on a diesel, they are so cheep and simpe its a no brainer as a first look. I'd go for a Coopers, Crossland or MANN if you get the choice, I wouldn't buy another UFI or whatever it was, and anything in a blue box should, as always, be treeted with suspision.