I've spoken to regular mechanics, and to Master Techs, no one has been any use whatsoever. One dealership told me not to bother bringing the car in, as they'd only check what I'd already checked.

See what your Master Tech says -

Loads and lots of diesel smelling smoke on startup - the colder it is the worse it is. Starts on the button, but chugs out load of smoke and it's very lumpy and difficult to rev until I drive off, then it's fine.

So far I've tried/replaced various things including -
4x new injectors, 2x new glo plugs, fuel pump's only 2 years old, no EGR, low mileage car (83k), a cold compression test was normal, no boost leaks, turbo recently refurbed... the list goes on.