Start-up blue smoke?

On start-up from cold, my 2.0 HDi (51 plate) xsara picasso emits a huge plume of blue smoke, On driving away, this clears after 30 yards or so. Thereafter, it runs well all day until it is left to cool off. I'm thinking blocked breather or similar, as I haven't had the car on the road for more than 3 weeks, and I am going to give it a full service ASAP.
I thought I would ask first, in case any other parts are needed.
Regards