Re: Pre-NCT service then failed!!
I failed on this recently as well as another issue, a friend failed on this only, both after full services including NCT 'pre tests'.
When my friend asked the mechanic about it, he said that the alignment easily gets misaligned, e.g. by going over speed bumps (even slowly), and that it must have happened between the service and the test. Funny though, that the last time I did an NCT I had it serviced something like 3 months before, so there should have been plenty of time for the misalignment to have occured.