1.6hdi, 2011, Engine smoke.

Hi everyone,
I've just joined the forum and I know here we go again with a newbie with a problem.
My daughter owns a 308 SW, 1.6hdi, on an 11 plate, I have been working on the car in prep for the MOT. The problem is blue smoke coming from the engine bay.
I have noticed that it appears to be coming from behind the oil filter housing, normally I would assume oil hitting the exhaust but, given that there is no drop in levels I'm kinda ruling this out. I know it could be from anywhere in that area, I have wrestled with the band/clamp on the cat, making sure it's correctly positioned and tight, but that hasn't resolved the issue. Would you advise removing the cat completely, and would this be a difficult thing to do? Also, a couple of other things, on a cold start the engine runs slightly uneven but when warmed up runs smoothly, the smoke stops but there are still fumes. There is no lack of power, there is no obvious issue with the turbo. So I'm now scratching my head. Any insight would be appreciated. On the whole it's a damn good car for its age and mileage.
Thanks in advance.