The other half has just rung me from a motorway services saying that she was in the middle of an overtake when all of a sudden there was a dramatic increase in noise from the air filter/dump valve (almost like someone had suddenly fitted an induction kit) She said there are no warning lights and car is running fine. Any ideas????

Check the airbox is properly shut, and check the intake hose is properly connected to the MAF and turbo intake pipe.

If the standard DV was leaking then you'd notice as you'd have a boost leak and it would probably kick into limp mode.

If you have checked everything and it's all good, then start to consider compressor wheel damage, and have the turbo inspected.

Thanks Bodge.

Try to keep it off boost until you get a chance to check the airbox and pipework is ok, if there is a large leak after the air filter you risk sucking insects, grit and all kinds of other things in through the spinning turbo which could knacker the compressor.

I told her to take it easy. Hopefully she listened!

Update: Her uncle took the engine cover off and it turned out to be the big hose to the dump valve had fallen off! Hopefully no damage!