Waves of nausea shake the body politic. Theresa May’s limitations as a leader produce such feelings of revulsion that at frequent intervals a spasm runs through her own party, which seems about to spew her out. And yet she is still in office. For although May is considered deficient in leadership qualities, so are her rivals. If Jeremy Corbyn were a formidable parliamentarian, the Conservatives would have had to ditch her by now. But although Corbyn has the quality of having refused to play the careerist game, he is a feeble debater and has yet to humiliate May at Prime Minister’s Questions, least of all on the issue of Russia.

When looking around for someone who could replace May, or indeed Corbyn, a problem arises. Few in either the cabinet or the shadow cabinet are seen by the public as potential leaders. Most of them are regarded – to the extent that anyone has heard of them – as career politicians who have never done anything in the slightest bit brave or interesting outside politics. Taken as a group, they appear industrious, conformist, pallid, selfish and dull.

Boris Johnson, Michael Gove and Jacob Rees-Mogg are the most conspicuous contenders for the Tory leadership, but each has bitter enemies as well as admiring friends. While May has preserved a precarious unity by being weak, the fear is that one of the three Brexiteers might split the party by being too bold. What other possibilities exist? They are more numerous than one might think. One of David Cameron’s forgotten services to the Conservative Party was to increase the number of women and ethnic minority candidates who stood in winnable seats. Conservative MPs are more diverse than when he became leader in 2005, and it is not inconceivable that one of these recruits will in due course become leader.

Over the same period, an even more unexpected development took place. Three ex-soldiers who are seen as potential Conservative leaders were elected to parliament, and so was one who may go on to lead Labour. Their names are Rory Stewart, Tom Tugendhat, Johnny Mercer and Dan Jarvis.

To understand the significance of this, it is worth glancing at the history. Between the Duke of Wellington, whose last brief premiership was in 1834, and Winston Churchill in 1940, not one prime minister had served in the armed forces. From Churchill until 1979, every prime minister except for Alec Douglas-Home (debarred by illness) and Harold Wilson (a wartime civil servant) had served in the military in either the First or Second World Wars, and so had hundreds of MPs.

Both Clement Attlee and Harold Macmillan had been badly wounded during the First World War. Their military service was of the greatest political importance. Nobody could impugn the patriotism of Major Attlee, who went on to serve loyally under Churchill, whom he greatly admired, in the wartime coalition, before defeating him in the general election of 1945 and taking charge of the greatest of all Labour governments, itself composed of many and various talents. Military experience is conducive to teamwork.

In an increasingly egalitarian age, it had another advantage. The First World War threw together subalterns from privileged backgrounds with men who had started with nothing. In the trenches they endured horrors of which civilians could have only the faintest idea. Here was equality of risk and sacrifice: indeed, even greater risk and sacrifice for junior officers than for the men they led. Anthony Eden, who in 1955 succeeded Churchill as prime minister, said that while serving in Flanders with men from his own district in County Durham, he acquired a “sense of the irrelevance and unreality of class distinction”. He became a One Nation Conservative: the creed with which Stanley Baldwin, who dominated Tory politics between the wars, sought to meet the challenge of socialism, while at the same time welcoming Labour into parliament and indeed into government.

For Harold Macmillan – under whose leadership the Conservatives recovered so well from Eden’s 1956 Suez debacle that they won a decisive victory at the general election three years later – the trenches were likewise a formative experience. To the end of his life (he died in 1986), Macmillan remained loyal to the men with whom he had served in Flanders 70 years before. In his maiden speech in the House of Lords, delivered in 1984 at the age of 90, he deplored the miners’ strike, then being fought by Margaret Thatcher, for whom he felt little affection: “It breaks my heart to see – and I cannot interfere – what is happening in our country today. This terrible strike, by the best men in the world, who beat the Kaiser’s and Hitler’s armies and never gave in.”

There sounds the lost voice of One Nation Conservatism. By the 1980s, even the Second World War generation of politicians was starting to pass from the scene. Edward Heath, a protégé of Macmillan, was an officer in north-west Europe in the 1940s, an experience that helped make him a fervent supporter of European unification: as prime minister he had in the early 1970s taken Britain into what was then the European Economic Community. Heath remained an MP until 2001, but was no longer of significance. James Callaghan, who served in the Royal Navy during the Second World War and in 1945 had appeared, like many Labour candidates, in uniform for his selection meeting in Cardiff South, became in 1976 the last of the wartime generation to reach 10 Downing Street. His air of benevolent authority was in its way very naval (his father had been wounded at the Battle of Jutland in 1916), and on a personal basis he was more popular than Thatcher, but she beat him in 1979 following the wave of public sector strikes known as the Winter of Discontent.

Nicholas Soames, who as a young man served in the 11th Hussars and is still a Conservative MP, likes to recall that when he was first elected in 1983, there were two members of the Tory whips’ office who had gone ashore on D-Day. On the Labour side, Denis Healey had been a beachmaster at Anzio, while senior Tories such as Lord Carrington and Willie Whitelaw bore, like Eden, the letters MC for Military Cross – as a silent but sufficient reminder that they had put themselves in harm’s way.

A few former soldiers such as Soames, himself a grandson of Churchill, still entered the Commons, but by the 1990s they were in a small minority, and none of them was seen as a future leader. The atmosphere now was civilian. Tony Blair had been a barrister; David Cameron a special adviser.

Yet the public became increasingly dissatisfied with this generation of career politicians. They appeared, in the mass, callow and uninspiring. In any pub in Britain you would hear the accusation that they were only in it for the money or that they were all the same – and in 2009, when the MPs’ expenses scandal broke, the charge seemed proven. Our political class stood convicted of lining its own pockets while having no idea of the struggles other people faced.

Anthony Eden (centre) servd in the First World War before going on to become Prime Minister. Credit: Getty

In 2011, the expenses scandal claimed as one of its victims Eric Illsley, the former National Union of Mineworkers official who was Labour MP for Barnsley Central. He pleaded guilty to three charges of false accounting and was sentenced to 12 months in prison. One of those who put themselves forward for his seat was Dan Jarvis. He faced what should in Yorkshire have been the insuperable hurdle of hailing from Nottingham, where the miners had kept working during the strike. But he was also a major in the Parachute Regiment, and when someone observed at his selection meeting that he had not run many political campaigns, he was able to reply that he had run a few against the Taliban.

It is hard to exaggerate how deeply the public prefer a former soldier, especially one who has seen active service, to a former lawyer, special adviser or trade union official. Jarvis was duly selected and returned for Barnsley Central.

Soon after he arrived at Westminster, another Labour MP who had served in the forces, the MP for Falkirk, Eric Joyce, who had risen from private to major in the Black Watch, got into serious trouble in a Commons bar. Most Labour Party members wanted nothing to do with Joyce. He was seen as an embarrassment, and was left to sink from view as quickly as possible. Jarvis saw this as intolerable, and did a great deal to look after Joyce, ringing him several times a day to find out how he was. A Conservative MP, Adam Holloway, who had served in the Grenadier Guards and had been at Sandhurst with Joyce, also did what he could to help. Here was a different scale of values: a man was in serious trouble, so you tried to rescue him.

You learn more about leadership in Afghanistan or Iraq than you do as an underling at Westminster. Sharing a cup of tea in the small hours in an outpost thousands of miles from home is a good way of getting to know your compatriots. At its best, military life encourages solidarity, self-sacrifice, courage under fire, making light of difficulties, and a willingness to back one’s own judgement. You do not abandon a comrade because the idiot has got himself into trouble. You rally round.

When Gavin Williamson, the new Defence Secretary, a man with no knowledge of or instinct for military life, tried to garner cheap applause by saying that we should “destroy and eliminate” Britons who had fought for Islamic State, Jarvis had the experience needed to put him right. As he wrote in the Guardian:

When on military operations, your proximity to death and violence – and to those who do not acknowledge the rule of law – both challenges your belief in the importance of such laws and reinforces the need for them… But how we utilise force is what differentiates us from our opponents. Soldiers know they lose their legitimacy when they sink to the level of the terrorists they face, and that such legitimacy is maintained through the rule of law. If soldiers understand that, secretaries of state should too.

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Johnny Mercer left the army after 12 years, having served in Afghanistan as a captain in 29 Commando Regiment. In 2015 he stood as the Conservative candidate in the Labour seat of Plymouth Moor View, and after the Tories polled the constituency, Lynton Crosby, the Australian strategist running their campaign, told him: “You ain’t gonna win, mate.”

But Mercer did win, and delivered a maiden speech in which he explained his commitment to better mental health provision and care of veterans. He recounted the cases of his friends Lance Sergeant Dan Collins, who committed suicide after returning from Afghanistan, and Lance Bombardier Mark Chandler, who was shot in the face while serving next to Mercer “in an intense close-quarter gunfight” during a dawn patrol, and died in his arms. Mercer spoke of “the bottomless well of grief that comes from losing a child, husband, brother or sister in war”.

This speech attracted much attention and Mercer was singled out as a potential future leader, which can be an invidious position, as it distresses other MPs. As he remarked in a recent interview: “I have no delusions about how some colleagues do feel about me, I’ve been told so. Recently I’ve done a lot of media on defence and the NHS; they genuinely think I do that for myself. They fundamentally miss the point that this is me doing my bit for the team effort.”

For Mercer, “the team” stretches across party boundaries: he has expressed his disgust at the sexist and anti-Semitic abuse thrown at Ruth Smeeth, the Labour MP for Stoke-on-Trent North.

When Tom Tugendhat – after serving with the army in Iraq, Afghanistan and as military assistant to General David Richards, then chief of the defence staff – applied for the safe Tory seat of Tonbridge and Malling in 2013, he was able to declare: “I am not a professional politician… I have never fought an election.” He judged, rightly, that this would be to his advantage; he won an open primary against stiff competition from three other finalists with greater political experience, who all went on to find other seats.

Although he only became an MP in 2015, Tugendhat was elected to the chairmanship of the foreign affairs select committee in the summer of 2017, after indicating, in a Times article, that he was determined to hold the Foreign Secretary, Boris Johnson, to account: “When humour is lost in translation it creates misunderstandings with other countries that we can’t afford.”

The Tugendhat insurgency – which routed the incumbent Conservative committee chairman, Crispin Blunt, who was thought to be too sympathetic to the Foreign Office – was supported by a cross-party coalition which included Michael Gove, Jacob Rees-Mogg, Keir Starmer and Dan Jarvis.

Rory Stewart served in the army for a short time, but became celebrated for his proconsular exploits in Iraq, where after the invasion of 2003 he played a role in trying to reconstruct two of the country’s southern provinces, and for his remarkable walk across Afghanistan, described in his book The Places In Between.

Soon after he was elected an MP in 2010, the New Yorker published a profile of Stewart, in which he described his idea of leadership by talking about his work with a charity he set up in Kabul:

I work with a local government councillor called Aziz, who was a champion wrestler. For 40 years, he has dealt with war, pogroms and government. He is assessed by members of his community on whether he is generous to the poor, courageous even in the face of death, a powerful representative of their interests and able to keep his promises. He and they believe that leadership is an exercise in moral virtue and courage, that politics should be a noble profession and politicians virtuous. A British voter might think that is naive. But I believe Aziz is right.

Most British voters would, I think, be delighted by such a definition of leadership, as long as they were confident the person making it was not a hypocrite. In the recent reshuffle Stewart was moved from the Foreign Office to be made prisons minister, which was said by some to be a ridiculous appointment given his expertise in foreign affairs. But it might equally well turn out to be a good one. Some of his early remarks, about the need to concentrate less on the theoretical aspects of prison management and more on finding out, for example, why Liverpool prison is filthy and getting the place cleaned up, have been encouraging.

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Leadership contests are unpredictable, and the chances are that none of these former soldiers will reach the top. But at least they are expanding the range of possibilities beyond the ranks of candidates who only know or have ever done politics. And it happens that Ruth Davidson, the Scottish Tory leader who many, especially on the Remain side, want to see succeed May, was an enthusiastic member of the Territorial Army. On becoming, last summer, honorary colonel of 32 Signal Regiment, in which she herself had served, Davidson declared: “The training you receive as a reservist develops leadership, decision making, teamwork, confidence and moral courage.”

Just the qualities one would like to see in a prime minister, since the greatest holders of that office (one thinks of Churchill and Attlee) have succeeded only by conducting a strong team of ministers. The prime minister cannot do it all on his or her own. They have to appoint good colleagues, trust them to do good work, and listen to them when they talk good sense. Cabinet government is not some impractical constitutional theory. It is the best way of reaching good decisions.

In the United States, soldiers since George Washington have shown that they can become statesmen by rising above the petty partisanship that disfigures so much of politics. In Britain, the public is disgusted by politicians who seem interested only in advancing their careers, and who display none of the qualities one looks for in a leader, including the ability to recruit and work with the best people for the job.

But the Commons is not a fixed body. It evolves, and one of the unremarked ways in which it has changed in recent years is by taking in gifted new members who learned about leadership in the armed forces, and not as bag-carriers to nonentities. l

The author’s new book, “Gimson’s Prime Ministers: Brief Lives from Walpole to May”, is published by Square Peg