Y does Britain need a Queen AND a Prime Minister?

The Queen is not a political advisor. She is a monarch and mainly ceremonial.

We need a bit of government theory, really, to explain it. Every country needs a head of state and a head of government. The head of state is the visible head of the nation, will have certain duties under the constitution including giving final approval to laws, and is the diplomatic host. The head of government is as it says - the actual head of the government who really has most say in running the country. All these jobs need doing in any country, it's just a matter of how you divide them up - or whether you divide them up at all.

I often find Americans don't understand this because the President doubles up as both. It was the first country in the world to ever have an elected combined head of state and head of government. But the majority of countries have two different people to do these jobs, and the UK is one of those. Most of Europe is the same (often with a purely ceremonial president rather than a monarch - like Ireland or Germany), and looking around the world I can think of a lot more.

If you're going to have a parliamentary system as the UK does, where the head of government sits in the legislature, you really need a separate head of state to sit over and above it all, even if their actual duties don't amount to much. At least that's the almost invariable model.

So the Queen is the national figurehead, she formally calls elections, she gives Royal Assent to Bills that get through Parliament, she appoints the Prime Minister and other Ministers, she opens Parliament each year with her Most Gracious Speech from the Throne, and in general represents the nation on formal occasions. On Remembrance Day every November, for example, she always lays the first wreath in remembrance of the war dead at the ceremony in Whitehall. Anyone who is required to swear an oath of allegiance swears it to her, personally. Essentially she is the non-political part of heading up the country.

While the Prime Minister actually leads the government and does what is more political. Where the Queen appears to do things that could be political, in reality she has no choice - she does not veto Bills because that would be undemocratic, the only real choice she has in who is Prime Minister is the leader of the party that got most seats in the House of Commons at a general election, and we all know she doesn't write the Throne Speech. (I wonder sometimes if she's thinking "who wrote this crap?" but NO way will she let on! It wouldn't be right. Which is why she always reads it out totally stony-faced.)

What happens at a state visit of the POTUS provides a nice illustration - and as Trump has been invited for one fairly soon, it's kind of topical anyway. He and the First Lady will be invited to stay at the Palace, the Queen will throw a state banquet in honour of her guest (where the after-dinner speeches will be strictly non-controversial and about what great buddies we are), they'll do all the ceremonial things like inspecting troops, and if the Secret Service didn't insist that the President uses his own armoured car, he would get a horse-drawn carriage ride to the Palace.

I remember a visit Reagan made. Someone must have had the bright idea that as he and the Queen are both horse-mad (Her Majesty is well known as a knowledgeable racehorse breeder), how about if they went riding together? OK, off they went to Windsor Castle where the Queen has stables, she lent him a horse and off they went. It looked great in the press.

But the Queen DOES NOT DO POLITICS, and of course the President hasn't crossed the Atlantic just for a nice time. He wants to talk politics, and a state visit will always include time with the Prime Minister at HER official home, 10 Downing Street. It's also possible for the President to pop over and see us without all the panoply of a state visit, by calling it a head of government visit. Then he's not "wearing his head of state hat", just his head of government hat, and that can be arranged much quicker. Obama did that last year - I remember because he made certain remarks about the EU that didn't go down well.

Britain doesn't need a Queen or a Prime Minister. The citizens of Britain want a Queen and a Prime Minister. The citizens overwhelmingly are in favor of continuing the monarchy. The duties of both positions differ as the Queen doesn't deal with the politics of government but rather deals with charitable endeavors and the Prime Minister deals with the House of Parliment and the political affairs both at home and abroad. Right now the U.S.A. needs a monarchy rather than what it has now, a dictatorship, with the head of State, Donald J. Trump, angering the entire world with his off the wall changes he's put into place denying people their basic human rights.

Yes, we do.

You don't want to be like America and Zimbabwe, do you?

For the same reason that we have plumbers AND electricians.

We don't need a Queen, its money for old rope, if they went tomorrow the running of the country would not suffer.

Because it WORKS!! We have Parliament, with Parties, a regular Election and so the Leader of that Party becomes the PM and responsible for the governing of the country (well that's the idea - these days politicians don't seem to be able to stop POLICKING even when elected to govern). On the other hand we have a Monarch who isn't elected, and isn't Political. She has the right to sack the PM if needed and the Government has the ability to decide whether the Monarch isn't able to carry out their duties, and so appoint a Regent.

We have a constitutional monarchy - and looking at America just now, THANK GOODNESS!!!

The Queen is the Head of State, and the Prime Minister is the Head of Government. Most countries separate these two jobs, unlike the USA, where the President does both.

Britain doesn't need a Queen. Britain doesn't need a lot of other figureheads as well, mayors and such. There are a lot of people who are paid for doing nothing relevant.

The Queen is there to sack the PM if he becomes erratic

Or should I say very erratic as being ordinarily erratic is quite usual.