So basically it breaks down like this.
In order to pass the tests all cars are subject to, it will pass with flying colours all TDI's will.
HOWEVER
If your pulled over by a particuarly arsey police man he CAN fine you for it and take your car off the road.
or
If your MOT'er decides he wants to make some extra money he CAN say your car isnt road legal.
Basically, if you know someone whos pretty good and does MOT's or people who are lazy, Just do it.
The police PROBABLY wont notice, their inspections are normally of the tyres, washer jets etc.
and an MOT'er PROBABLY wont fail you for it.
The chances are always there however.