Flawless craftsmanship, brilliant indeed! A political song that says what it wants to say, without unnecessary invectives.

Perhaps you should not use the word "rule" for the current monarchy, which has as little power as that abstract "Britannia", or the "we" of the populists.

Another aspect: these days are not ideal for launching the song. Compared to the sheer madness in government and parliament, the monarchy looks like a harmless bargain, given its decorative value. "Pennywise and poundfoolish" now translates "millionwise and trillionfoolish" - the "Brexit bill" that comes immediately after the dinner will be only a small fraction of the overall costs, no matter what the "deal" in terms of billions.