There will be a vote of no confidence in the prime minister of the UK today, but it is limited to Conservative MPs only and requires a majority of them to pass the motion. None of the media coverage I saw explained why the vote is limited to Conservative MPs. If the vote is open to the opposition as well, there will be a very good chance for the PM to lose. So what is the justification for this limitation? Why can't the opposition vote?
Because it's not a vote of confidence in the Prime Minister, it's a vote of confidence in the Leader of the Conservative Party, who also happens to be the Prime Minister. See the announcement from the Chairman of the 1922 Committee, Sir Graham Brady:
The threshold of 15 per cent of the parliamentary party seeking a vote of confidence in the leader of the Conservative Party has been exceeded. In accordance with the rules, a ballot will be held between 1800 and 2000 TODAY MONDAY 6th JUNE — details to be confirmed. The votes will be counted immediately afterwards. An announcement will be made at a time to be advised. Arrangements for the announcement will be released later today.
The vote is being held under the rules of this committee - made up of all Conservative party MPs. The full process of the confidence vote and any subsequent leadership election is explained in this House of Commons Briefing Paper here. If Boris Johnson is unsuccessful in a confidence vote, he will remain as Prime Minister until a new Conservative party leader is chosen, who will then be invited by the monarch to form a government and take over as Prime Minister.
I want to clarify one thing: It is possible for a Parliamentary vote of no confidence to be held, in which case the entire parliament would be voting for the fate of the government, including the opposition. Such a vote can be called by the leader of the opposition, who in this case would be Keir Starmer.
One reason I wanted to clarify this was that Boris Johnson had almost 150 of the conservative MPs vote against him, and it is such that Johnson's majority in Parliament is only around 40 or so MPs. It would not be impossible or even unlikely that in the event of a Parliamentary vote of no confidence, enough of these MPs would vote against the government for the vote to succeed. In this case, either the government must resign or the PM must ask the Queen to dissolve parliament such that new elections can be held.