Boris Johnson's resignation and the UK constitution after he leaves

They will say the ability of Tory colleagues to oust a failing leader is a testament to the robustness and enduring value of the Westminster system of parliamentary democracy.

On the latter point, they might even be right. The British parliamentary system provides ­multiple “break-points” at which a prime ­minister can lose office. They can lose a general election. They can lose a majority in the House – whether through defections or by-elections. Most of all, they can lose the support of their own Cabinet, and their own ­parliamentary ­party, without which they are unable to ­continue in office.

In this regard, British parliamentary ­democracy compares favourably with the US presidential system, which made it effectively impossible to get rid of Donald Trump (above) before an election.

However, this comes with three strong ­caveats.

Firstly, some Johnson allies have attempted to subvert the basis of the parliamentary system, presenting the system as if it were quasi-presidential. Johnson claimed a “personal mandate”, direct from the electorate, which would make it “undemocratic” for the House of Commons or his own party to remove him.

That claim is spurious. In a parliamentary democracy, the right to hold government office comes from, and is subject to, the confidence of the elected House. To deny that, with claims of a “personal mandate”, is to undermine the key accountability mechanism – the vote of no-confidence – on which the whole system is based.

But without a written constitution to clearly articulate that principle and to translate it into clear, enforceable constitutional rules, people can make these kinds of strange claims and it is difficult to contradict them.

Without the formal structure of a written ­constitution to hold it in place, the British ­system is flexible – but in all the wrong ways. It flexes in response to the mutations and ­distortions imposed upon it by those in power. It bends to their will and accommodates their vanities.

The second caveat is that the ability to ­(eventually) drive a truly terrible leader out of office is a very low “threshold of success” for a democratic constitutional system.

Democratic constitutions perform a variety of functions. They proclaim the ­foundational ­values of the state, so that there are some ­guiding and grounding principles and a shared civic basis for national identity.

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They organise and regulate public ­institutions, legitimating the exercise of public power, and making the relationship between these institutions stable and predictable. They establish ­robust democratic mechanisms of ­representation, to ensure inclusion in decision-making. They also enforce the ­accountability and responsibility of the governors to the ­governed – providing not only ways to get rid of a government, but also to challenge and ­scrutinise their actions.

Protecting the independence and neutrality of institutions like Civil Service Commissions, Judicial Appointments Boards and Electoral Commissions, free from partisan control, are just some of the ways in which constitutions separate the party-political, policy-making, functions of the government from the permanent, non-partisan structures of the state.

Constitutions also distribute power and ­resources territorially, between different ­levels of government. They protect fundamental rights, and establish guarantees for particular minorities or communities who might not be ­adequately protected by simple majoritarian politics. They can even try to police public ­ethics and to orientate the state to particular public-regarding policy goals, so that governments are constrained in various ways to ­abstain from ­corruption and to focus their efforts on ­promoting the common good.

Seen against that checklist, the “British ­constitution” is not doing so well. Attacks on ­human rights and the judiciary, the erosion of institutional neutrality through attempts to ­politicise the civil service and to capture the Electoral Commission, high-level corruption, and the undermining of devolution, are just some of the many instances of constitutional breakdown.

Thirdly, it is not even very good at getting rid of wayward prime ministers. Boris Johnson has not actually resigned. Sir Keir Starmer intended to move a motion of no confidence to oust him. Yet the Government refused to allow it, and in the absence of formal written constitutional rules, there was no way to enforce this core ­parliamentary principle.

Perhaps the next prime minister will be a ­better person and let us hope that is so. Still, it is folly to entrust the well-being of the state to the character of particular individuals.

It might be too late to save the UK, but the states that emerge breakup of Britain should heed this lesson in their new constitutions: ­slippery rules beget slippery practices.