Whiffs of diesel / breather problems in mk2 Octy vRS diesel

I've got a mk2 Octy vRS diesel, first of the common rail variety, on an '09 plate. I'm currently getting occasional whiffs of diesel in the cabin, the odd split-second throttle lag when changing down through gears, and today while idling at lights the car started to stutter to the point it was making the car shake. No noticeable patterns (hot / cold / different weather conditions), but the car can occasionally refuse to restart if the engine's just been switched off unless I also add some revs.

Otherwise car had a service reasonably recently by a trusted mechanic (that deals regularly with VAG cars and vans) and has 120k on the clock. Oil and coolant levels are fine and I run Redex with practically every tank of fuel.

My initial thoughts are it's a split breather hose somewhere (although I can't find anything on initial inspection), but was wondering if there's any other common faults that would have the similar symptoms. 

Anyone wiser than yours truly care to have a crack at enlightening me?

Edited 29 April, 20179 yr by Pimpmaster Jazz