My next door neighbour is an NCT inspector(Drog)....he said they're not failing them as long as the seats can move...and they haven't failed any yet,
In the NTA guideline PDF,it doesn't say that the screen can't be attached to the headrest but that the movement of the headrest is not restricted,
When getting my daisies refitted last week the two lads from the NTA said they weren't a fail at suitability,i told them i had a screen but removed it in case there was a problem,they said that they had encountered a couple of homemade screens of very poor quality(only behind the driver) and quite dangerous looking.