Other than the ability to survive votes of confidence, are there any rules on who may or may not be Prime Minister of the UK? E.g. could the monarch be the PM? Could a non-UK-national? Could a minor?

1 Answer 1


The UK constitution is based, in part, on tradition and convention.

By tradition, the Prime Minister must be a member of the House of Commons. As such they must be 18 or over and a British, Irish or Commonwealth citizen. They cannot be a noble, though it is possible to renounce one's hereditary position in order to stand for Parliament. The Queen is also not a commoner, so can't be an MP in the House of Commons, and so can't be Prime Minister. Certain other people are not eligible to be an MP: Civil servants, Police Officers, Judges, Bishops, Soldiers, though they are free to become MPs (and PM) after leaving their post.

However, the advantage of an unwritten constitution is that it can be bent as the need requires. There is no written constitutional requirement for a Prime Minister (although many recent acts of Parliament refer to the post) The title is unofficial (and began as a term of derision); the official post is "First Lord of the Treasury". So there is no written rule that says the PM must be an MP, there is no written rule that says the Queen can't pick her favourite horse to be PM.

But you shouldn't interpret this to mean that the Queen has a free hand to pick whoever she chooses. Tradition is as important to the UK constitution as the Supreme Court is to the US constitution. To ignore the strict requirements of tradition is as incorrect as ignoring the rulings of the Supreme Court in understanding the Constitution of USA.

So short answers are

  1. No, the Queen cannot be PM
  2. Yes, a foreign national can be PM (if they are Irish, or from a qualifying Commonwealth country)
  3. No, a child may not be PM.
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    Re commoners: "Although popularly considered to refer to the fact its members are commoners, the actual name of the House of Commons comes from the Norman French word for communities – communes." (source). Not all MPs are commoners; some of them are knights and, as you mention, hereditary peers. Commented Aug 16, 2019 at 21:54
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    Re people not eligible to be MPs: it might be worth clarifying that people can't continue to serve in those roles while being an MP, but former holders of those posts can become MPs. Commented Aug 16, 2019 at 21:56
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    @SteveMelnikoff that is interesting, Knights are "gentry" not "nobility". The Queen can't be an MP because she is the Queen, and the Queen can't be an MP. Let's not overthink this!
    – James K
    Commented Aug 16, 2019 at 22:06
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    Isn't over-thinking things the point of this website? :-) Commented Aug 16, 2019 at 22:13
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    en.wikipedia.org/wiki/Alec_Douglas-Home?wprov=sfla1 is an example (within living memory) of how far the constitution can be stretched to accommodate a PM who is not currently an MP (or eligible to be one)
    – mikado
    Commented Aug 18, 2019 at 21:08

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