Failed smoke acceleration test pre-MOT

[Mickeyluv]

I noticed recently when accelerating hard I was leaving a smoke trail. Also, at idle the exhaust smells really acrid and I now have a slightly sooty rear bumper. Even just slightly blipping the throttle causes visible smoke, but there's nothing visible when driving normally at steady speed. As my MOT is nearly due I took my car to have the emissions checked and the readings are;

K1 7.71
K2 7.53
K3 5.44
K4 3.92
K5 6.51
K6 5.66

The mean value came out at 5.85 and the pass limit is 3.00. This gives me a short window in which to get the down below 3, if economical to do so. The car is a 1.9TDI automatic B5.5 from 2005 with AVF engine. The car runs and pulls well and a 110 mile run up the motorway a few days ago averaged 58.4mpg. Around rural lanes and B roads I'm getting 46mpg.

So far I've;

Checked the fault codes - just one for a missed ABS pulse
Cleaned the EGR and checked operation off the car - works fine.
Checked the vacuum to the EGR - nothing from cold startup then slight vacuum under idle conditions when engine warmed up.
Checked the flexible hoses for splits and removed the lower intercooler hoses to inspect off the vehicle.
Checked the anti-stutter valve remains open during engine running.
Filled up with V-power diesel and added two bottles of Wynns 'Clean Burn' diesel smoke treatment
Did a couple of Italian tune-ups - one of these immediately before the smoke test.

The intercooler had a small amount of oil pooled in the bottom - I understand that this is normal for this engine.

Right now I don't know what else I should check.