The reigning monarch in the UK is the Head of State
The Government is His/Her Majesty's Government. He/She is the Head. The monarch is still required to sign every piece of law, and can refuse to sign and piece of law. Although this refusal has not happened for a long time.
Unlike most countries, the UK does not a a written constitution (one single document). The constitution is wrapped up in many documents, statutes, traditions, and recognised practices. It also can and does change.
Regards the word 'royalty', I think it is generally treated as an uncountable noun.
He is royalty
They are royalty
But there are exceptions, which is why I used the term 'generally'.
yeah, gough whitlam was sacked by the GG john kerr, that is the fact. whitlam's commission as prime minister was withdrawn under section 64 of the Australian Constitution and Malcolm Fraser was commissioned as a caretaker prime minister, again by kerr. :-)
there was another incident regarding royal reserve power but on a state level, i think. it was the queenland governor Walter Campbell who refused to 'exercise vice-regal authority' on the advice of the Queensland Premier Joh Bjelke-Petersen, making the Premier's position as a 'leader' of his own cabinet look absurd. :-)
I stand corrected, I was ill informed about the circumstances. I have been told the the GG threatened to dissolve parliament and Whitlam resigned.
I was wrong, Mae Culpa