There is no fixed or predetermined role for former prime ministers in Britain. What they do after they leave office depends very much on personal choices and on circumstances. Few former PMs leave Number 10 Downing Street as happy, contented or fulfilled people, or at a time and in a manner of their own choosing. They mostly have a deep need of the "political game" and find giving it up, or being brushed to one side, very difficult and frustrating — so David Cameron's experience is not unique.
There were only two cases of former prime ministers serving in other Cabinet positions after losing power, in "normal" peacetime conditions of single-party government in the twentieth century (other examples occurred during wartime coalition governments). One was way back in the 1920s. The most recent was Alec Douglas-Home, who had only a short tenure of one year as Conservative PM 1963-64. He went on to serve as Foreign Secretary in 1970-74, in the government of Edward Heath, and played a dignified "elder statesman" role in the Conservative Party. The way in which Alec Douglas-Home handled the transition from prime minister and party leader to being a secondary figure without public bitterness or rancour greatly enhanced his reputation, and was a key factor in allowing him to carve out a constructive post-leadership role.
We know that another former prime minister, Edward Heath, wanted Margaret Thatcher to make him Foreign Secretary in 1979 when she became PM, but she had other ideas — offering him instead a job 3,000 miles away as ambassador to the USA, which would have meant a sort of exile; he took the message but refused that job!
It is difficult to seriously imagine David Cameron coming back as Foreign Secretary under another prime minister. There is no real chance of that happening under Theresa May. He still has many enemies in the Conservative Party (unlike Alec Douglas-Home in the earlier period I mentioned). As the man who called and lost the EU referendum, so triggering Brexit, he carries a lot of negative "baggage".
To become a government minister again he would need to become a Member of Parliament again and win an election in a constituency, or be appointed to the House of Lords. Up until recently former PMs often became Lords (or a Baroness in Thatcher's case) — but Edward Heath, John Major, Tony Blair and Gordon Brown did not go to the House of Lords. The modern requirement for members of the House of Lords to declare the sources of their outside business earnings may be a deterrent for former PMs and leaders who have lined up lucrative directorships and consultancies etc.
Cameron has been writing his memoirs and is reported as having a £800, 000 contract for his book. This is much less than Tony Blair, who negotiated a deal worth £4.6 million for his memoirs; Thatcher's brought her in £3.5 million. I suspect that more copies of books by former PMs are bought than are read from cover to cover. These books can be hard-going and even boring — no one reads them for fun.
The views expressed in this article are those of the speaker, and do not necessarily reflect those of Sputnik.