It is not hard, the columnist David Aaronovitch remarked the other day, to be an outstanding performer on Labour’s front bench. He proceeded to praise in high terms the start Sir Keir Starmer has made at holding David Davis, the Brexit Secretary, to account.

Starmer’s debut is certainly noteworthy. In the letter he and his shadow cabinet colleague, Emily Thornberry, sent Davis a week ago, in which they posed 170 questions about Brexit, they also quoted two Conservative MPs, Andrew Tyrie and Dominic Grieve, with approval.

Grieve, they reminded Davis, had said: “The idea that a government could take a decision of such massive importance without parliamentary approval seems to me to be extremely far-fetched.”

ConHome put it to Grieve that Starmer is trying to seduce him. Grieve replied that he has seen no sign of seduction, but added that having accepted the outcome of the referendum, he had “a very strong feeling” that options to do with our future relations with the European Union “were being closed down without discussion”.

By insisting on having the discussion, Starmer may well, in Grieve’s words, “have been pushing at an open door with some Conservative MPs”.

Though by no means all of them. Asked if he regards Starmer as formidable, Jacob Rees-Mogg replied: “He is clever, but is, I think, taking Labour down the blind alley of opposing the referendum result. This makes him less formidable.”

Starmer himself insists he is not leading the way down that blind alley, and that he accepts the outcome of the referendum: “There is a mandate for the exit. There is no mandate for the terms.”

One can see him striving to make his case in such a reasonable and consensual way that it becomes difficult for people well beyond Labour’s ranks to disagree with him.

So in his first exchanges at the dispatch box with Davis, Starmer proclaimed our “duty” to “put the national interest first”, and remarked that “this should not be about point-scoring”.

Davis agreed the “issue is too important for point-scoring”, while Iain Duncan Smith, who on Monday of last week described Starmer as “a second-rate lawyer”, on Wednesday “unreservedly” withdrew that allegation.

It is certainly wrong to call Starmer a second-rate lawyer. He served from 2008-13 as Director of Public Prosecutions without attracting criticism of that kind.

According to a lawyer who knows Starmer well, Professor Philippe Sands, “He is knowledgable, well-prepared, balanced. He will shred Davis, Fox and Johnson, who are none of the above.”

It is certainly more than likely that Starmer will go through everything Davis, Liam Fox and Boris Johnson say, or have said, will collate any inconsistencies, and will seek to demonstrate the Government is in a mess.

Grieve, who served as Attorney General from 2010-14, said: “I have a high regard for Keir. Obviously we worked closely together. He was very effective at running the Crown Prosecution Service. Thoroughly professional.”

The real question is whether Starmer is a first-rate politician, and about this it is too soon to reach a verdict, for he was only elected to the Commons in May 2015, having the year before won the Labour candidacy in Holborn and St Pancras, where Frank Dobson was stepping down.

But in his current role, not being an experienced politician is in some ways an advantage. He did not serve under either Tony Blair or Gordon Brown, and is hard to place in the factional strife which rends the Labour Party.

Starmer is a cautious lawyer, which is a better and more reassuring thing to be than a tribal infighter so obsessed with stabbing the leader of some rival gang in the back, that he or she ceases to care about offering a credible alternative government to the Conservatives.

He is a friend of Ed Miliband, and must have hoped after the 2015 general election to serve under him in government. Starmer instead found himself a shadow Home Office minister under Jeremy Corbyn, responsible for developing a new immigration policy.

This summer, along with most of Corbyn’s shadow team, he resigned. But he did so “with great sadness”, and without burning bridges.

Starmer is by temperament a bridge-builder. He prefers to be the insider, welcoming everyone in, rather than the angry outsider, hurling abuse at the powers that be. In September, when the Labour membership chose Corbyn for a second time, backing him rather than Owen Smith by a decisive margin, Starmer recognised the result in a tweet of surpassing banality, but unimpeachable common sense:

“Congratulations Jeremy. Well ran Owen. Now it’s time to pull together and focus on the challenges ahead.”

Within the Corbyn camp, there was a growing recognition that Labour “needed to do something on Brexit”. People like Diane Abbott were strongly in favour of bringing Starmer in, as was Lord Falconer.

Thornberry, the previous holder of the Brexit portfolio, was furious she was going to lose it, but at least reckoned if it went to Starmer, she didn’t lose face. And in any case, she is now shadow Foreign Secretary.

John McDonnell was unhappy with the appointment, which offers Starmer the chance to outshine him, by giving a virtuoso display of how to oppose the Tories while at the same time reassuring middle England.

Future leadership contenders on the centre right of the party are similarly miffed. To them, Starmer is a 54-year-old beginner in a hurry, who has jumped the queue to be the next leader by shamelessly agreeing to serve under Corbyn. They consider him intolerably ambitious and self-regarding, instead of a proper politician with a coterie of mates who will put the boot into rivals.

But who is he really? His “Guardian-reading, Labour-leaning” parents called him “Keir” after Keir Hardie, the first Labour MP and leader. In an interview with the Guardian, Starmer said he eventually become very fond of the name, but this was not always the case: “When I was at school, at about 13, I thought, why couldn’t they have called me Dave or Pete?”

While Hardie was from Ayrshire, Starmer is from Surrey. His father was a toolmaker and his mother a nurse. He is one of four children: the others went to comprehensive school but Keir passed the 11-plus and went to Reigate Grammar School.

At Leeds University he took a first in law. He has joked that as each of the children left home, a donkey moved in to replace them, for his parents were deeply committed to saving donkeys.

Starmer spent a year doing further legal studies at Oxford, after which he qualified as a barrister and had a very successful career at Doughty Street Chambers, which he co-founded with Geoffrey Robertson, Helena Kennedy and others.

His hobby was and is playing football, which he perhaps takes even more seriously than his skill warrants. On a very hot day, when no one else could be bothered to do stretching exercises, he still did.

He also has the strength of mind to go for a drink after a game, but then return to work rather than drink late into the night. He supports Arsenal. In 2007 he got married to Victoria Alexander, a solicitor, and they have two children.

From this rather bare summary, he emerges as an exemplary member of the North London ruling class. In every field – the law, his constituency, even football – the work is done with the same unwearying energy and friendliness.

Starmer has said that if you find that the junior people in an organisation are happy, you can tell it is well run. When he took over as the head of the CPS, he toured all its branches, and managed to speak to almost a third of its 9,000 staff.

A fellow lawyer describes him as a team player, who masters his brief before he says anything: “I really trust him.” In order to test a point, Starmer will run it past someone he knows will disagree with it.

He is a liberal-minded lawyer with a disposition to help the underdog, where necessary for free. He was heavily involved in work to remove the mandatory element in the death sentence in Caribbean and African countries, and earlier this month visited Taiwan on the same mission.

But at the heart of his legal work lies “the principle that human rights apply to everyone equally”, as he put it in his maiden speech in the Commons. He argued the continuity from Magna Carta (of which four copies were being displayed at the British Library in his constituency) to the United Nations’ Universal Declaration of Human Rights, described by Eleanor Roosevelt as “the international Magna Carta of all men everywhere”.

As a lawyer, his commitment to equality is defined much more in terms of rights than in any economic form. He believes in freedom of speech, to which Labour politicians of a more authoritarian outlook play not much more than lip service.

So in an era in which Labour may continue to be quite weak, Starmer would be better placed than some to form a coalition with other liberal-minded parties. He might also be better suited than some more sectarian figure to the task of holding Labour itself together. People who dream of forming a new social democratic party find him intensely annoying, for they realise he will not help them to destroy Labour.

But such thoughts are premature, when we do not yet know if he can make big political decisions, or impress himself on a wider public. He is likely to be brilliant on the details of Brexit, which are such as to flummox many minds.

There comes a point, however, when the detail is not enough, and is perhaps even a distraction. It is possible to imagine, as the Financial Times just has, that he will become the darling of the Europhiles who wish to persuade us that Brexit is simply too dangerous.

But at that point a very big, and in its way very simple, decision has to be taken. Do we go forward or back? A lawyer works for, and advises, a client. A leader has to be able to make choices.