Black plume of smoke from exhaust on cold start

My 2005 diesel A4 spurts out a fairly significant belch of black smoke on a cold start. 30 seconds later it's all fine. The car is in good shape and regularly serviced by trusted people. I have heard that this is a characteristic of diesel engines but I'm sure it has got worse on mine. The car has almost 200,000km on the clock, quite a lot.

What's going on? Have I any cause to be concerned?

Thanks.

I don't know the ins and outs of that model, but I do know the Mercedes 200 series diesels had this issue, due to a malfunctioning recirculation valve (meant to send the smoke back for another burn before being emitted) It might be a worth looking into.

Will do, thanks.