Injector seals / leak from the turbo to exhaust joint if the turbo has been disturbed / leak from the DPF if it's really blocked (although I would expect the light to be on if this was the case) / leak from the EGR to cooler joint if it's been disturbed.

My 307 was smelly, because of leaky injector seals - there was some build up of tar, but no chuffing noises. Been fine since they were done. I'd find someone who actually knows their way around this engine - try a local Cit / Pug specialist.

Update is that the change of EGR valve has definitely helped the fume issue rather noticeably but there are still some fumes (of a... sooty/smoky variety) getting inside the car..

I spoke with mechanic. He said injectors were not chuffing but that if there was a lot of pressure caused by clogged DPF it could nevertheless cause some escape of gas via injectors. Any thoughts?

He said there were definitely no leaks anywhere in exhaust and that the clogged DPF was probably 'back pressuring' and that it could be 'oozing' gases as a result of the pressure.

So... he sees an artificial regen as being the way to solve the rest of the fume issue (though apparently doing this is not straightforward as my car is giving his computer false readings which won't allow the regen to go ahead... but I'll leave all that for another time!)

I know little about cars and am fearing the prospect of many pounds leaving me... and no improvement occuring.

So... IS it feasible that artificial regen of DPF will stop the remaining fumes getting into the cabin?

When I experienced fumes inside the cabin of my CRV it was a split in the EGR pipe (in the concertina part). The pipe was replaced and that fixed it

If the DPF is really blocked then it can leak exahust fumes out of the joint between the CAT and DPF, but I would expect to have a warning light and driveability issues. If it's as bad as you say it is, then it should be obvious just by doing a visual / smell inspection under the bonnet as to where it is coming from. Take the engine cover off, and start the engine, then have a a good look / smell around the injectors - if bad you may see smoke, and you will certainly smell it.

Thanks for the last two replies, guys. Will take back to mechanic with all that in mind.

A further question! In my perception, the nature of the smell is a little... sooty, not just exhaust fumes. Could that point all the more towards a leak from DPF?

55 plate, 81k miles. Only owned the car for a few weeks and have avoided driving it because of the fume issue. Car mostly runs well, though occasionally holds back a bit as pulling away, then comes to life at higher revs...

Other info: EGR valve had been stuck open, was replaced a week ago. I understand this may have contributed to the DPF clog.

Also: Pat fluid is showing as empty when car is hooked up to mechanic's computer. But there's actually plenty of Pat fluid!

Also, mechanic's computer is being prevented from initiating DPF regen. He will need to swap some box or other in the car to go ahead with regen, apparently. I wonder if something has been preventing passive regen ever happening!

Am becoming very inclined to sell the car, now! I would declare the issue when doing so of course (it's not immediately obvious on a test drive - I missed it!). Whatever I do, I'm losing a lot of money... sigh! I hope to minimize that by taking the most cost effective route forward in terms of repair, or by selling the car as is asap.