It’s fair to say Rishi Sunak’s decision this week to appoint David Cameron as the foreign secretary came as a surprise to many in Westminster. Not least because he hasn’t been an MP since September 2016.

So, do you have to be an MP to join the government – and how will David Cameron be held accountable by parliament if he’s not sitting in the House of Commons?

Can you be a cabinet minister without being an MP?

Strictly speaking, the prime minister can appoint anyone to the cabinet, whether they’re an MP, a peer or an ordinary citizen.

But in a parliamentary democracy like ours, it’s expected that members of the government will be held to account by at least one chamber – either the House of Commons or the House of Lords.

Becoming a member of the House of Commons (i.e., an MP) is normally only achievable at a general election or a byelection.

If a Prime Minister wants to appoint a specific person to the government who is not in either House of Parliament, it’s not very practical to wait for an election – which their preferred candidate might not win anyway.

Prime ministers in this position can use their power to appoint members of the House of Lords to get round this problem. Unlike MPs, there’s no election required so the decision can take effect almost immediately.

And that’s what Rishi Sunak did this week to bring David Cameron into the fold: the ex-Prime Minister is now, by appointment of the King, a baron for life.

How are ministers held accountable if they sit in the House of Lords?

The overwhelming majority of cabinet ministers are MPs, meaning they sit in the Commons and not the Lords. This has been the norm in recent decades.

Though it’s not unusual for junior ministers, i.e., members of the government who do not sit in cabinet, to be Lords. In fact, every government department appoints a member of Lords as its representative to help draft laws to pass through the upper chamber. Those (usually junior) ministers have to answer questions on behalf of the government and represent the government in debates – as do their counterparts in the House of Commons.

As Dr Alice Lilly of the Institute for Government think tank explained in an article, arrangements for holding cabinet ministers accountable in the Lords are “more complex” than those for junior ministers, “in part because it is relatively unusual for members of the Lords to hold such senior ministerial roles”.

The nature of the scrutiny they face is different too, she says, and can sometimes be higher in the Lords “in part because of the range of expertise and level of experience that many members […] have”. Dr Lilly notes as an example that “as a foreign secretary in the Lords, Cameron will be facing four of his predecessors (David Owen, Douglas Hurd, William Hague and Philip Hammond).”

However, there is another thorny question at the heart of this appointment.

MPs in the House of Commons are elected representatives of their constituents, while members of the House of Lords are not. And members of the House of Lords cannot enter the chamber of the House of Commons.

This is one of the reasons that it’s become the norm for senior members of the government (including the Prime Minister) to be drawn from the Commons. It means those leading the government, and those tasked with scrutinising it, are directly accountable to the public at the ballot box.

If Lord Cameron can’t appear before all MPs, it means that the line of democratic accountability (voters elect MPs, MPs scrutinise ministers) becomes more circuitous. This isn’t normally an issue with junior ministers in the Lords but is more significant when we’re considering one of the great offices of state.

Which is why the Speaker of the House of Commons, Lindsey Hoyle, said this week that he was seeking advice from the clerks who help run parliament on how best to make sure elected MPs can hold the new foreign secretary to account. Exactly how that would work is not yet clear, but Lord Cameron has confirmed that he will appear before committees of the House of Commons, which are run by small groups of MPs – though not in the chamber itself.