I took my dooper in for its service and mentioned the above problem. Turns out that engine fumes had been leaking from the turbo and it would require a new one. Hopefully come tuesday it will be all sorted.
Don't wait till the service - get it done now. Firstly because it's definitley not normal (though fairly frequent ) and mainly because you will be inhaling gases until it's sorted! Turns out it is due to a badly-fitted clamp between the turbo and the particle filter housing. They may order a new clamp, but chances are the joining surfaces are slightly warped, and will continue to leak a bit. The only real remedy is to change both the turbo and the pre-cat (primary catalytic converter).