LOM,
I can confirm that. The FA2 HUD was assessed by Boscombe Down to be carrying 'primary flight display information' quite late on in its test programme. First one as far as I am aware, but happy to be corrected.
BD then recommended a (highly expensive) programme of software analysis, which the MoD agreed to fund. After 6 months (having spent most of the dosh) they reported that they couldn't carry out any software analysis.
Great result - not.
Military aircraft cockpit display design (and certification) is one of those somewhat arcane areas where each major country has its own rather firmly held set of standards, opinions (or prejudices - take yer pick), over which fairly endless discussions can be held. In some cases, influential test pilots with strongly held opinions can be, well, influential. Add in the known fact that asking five pilots any question results in at least 6 answers can make delivering an 'acceptable' cockpit a bit of a saga.
As far as I know, HUDs have been classed as primary flight displays for some years now.
Happy New Year to all those sorting out the displays,
Engines