Pardon my ignorance but I thought there were seven major areas within the Non-Technical Skills.
You thought wrong. There are 8.
Someone in my box had one recently and while it was still non tech - they were associated with the job. So rather than "Talk about a time when you have had to communicate a message" It was more like "you have had a spad and on the phone to a CoSS - how would you deal with the situation. Not looking for the rules or regs but how you would use the Non tech skills to deal with that situation, and then he had three or four box specific rule questions.
This is correct. There are actually 2 questions per NTS, one for external and one for internal candidates (with a signalling background, platform staff applying internally won't be asked the technical NTS Q).
It is the interviewer's discretion as to which question they ask an internal candidate, so at my last interview, I was asked 6 technical and 2 non technical questions.
Also bear in mind that the Internal questions are NOT technical in nature. They do not ask "A train SPADs a signal, what do you do?" because you should know. They ask you more about the psychology of your reaction, because they will actually be asking about how you deal with pressure, for example.