When Boris Johnson’s new chief of staff in Downing Street first saw the girl he was to marry, the two of them were on a Reform Synagogue Youth (RSY) summer camp in Israel.

But the pair were just friends until Mancunian Dan Rosenfield, a long-time RSY activist, discovered that Jessica Brummer was working as an organiser for RSY in London.

And as his father-in-law, the leading city journalist Alex Brummer, recounted: “Dan’s idea was to ask her out on the pretext that he had a great venue for an RSY event, and he needed to show it to her”.

That was their first date. Fifteen years later the couple have three children, a strong sense of Jewish family, and Mr Rosenfield, a former senior Treasury civil servant, who counts Labour’s prime minister Gordon Brown, chancellor Alistair Darling, and Lord Darling’s Conservative successor George Osborne among his bosses, is about to embark on perhaps the biggest challenge of his professional career.

Not only was he head-hunted for this most public of positions — an “inspired appointment” according to Lord (Daniel) Finkelstein — but Mr Rosenfield has combined his professional life with a hands-on role in the Jewish community, as chair of World Jewish Relief, the humanitarian charity, since 2016.

Just 42, Mr Rosenfield is the son of a north Manchester dentist — his parents have since moved to Brighton — who spent his teenage years happily involved in RSY, including a year in Israel, milking cows on kibbutz. The family were members of the Shaarei Shalom Synagogue in Manchester, and in London, Mr Rosenfield and his family belong to Alyth Gardens (North West Reform) Synagogue.

He attended the prestigious Manchester Grammar School and then read modern European studies at University College London, specialising in German and philosophy.

Part of his degree — in which he achieved first class honours — included a year abroad. As an obsessive Manchester United fan, he chose Munich, telling the Jewish Telegraph in an interview last year that he had picked the city because “I wanted to go to a big town, and decided to go to Munich as Manchester United were drawn against them in the European Champions League group stage that season”.

In Munich he shared a flat with four German students, who all had different interests — from film, to handball, to antiques. He recalled:

“My overarching memory is making good friends — some of whom I’m still friendly with today.”

Twenty years ago, after graduating, Mr Rosenfield landed his first job as a policy adviser in the Treasury, working his way through the civil service and eventually becoming principal private secretary to Alistair Darling.

It was, says Alex Brummer, “a powerful job, because all communications go through the Treasury”.

During that period, around 2007, he met and became friends with his counterpart at the Foreign Office, who became British ambassador to Israel.

According to the former ambassador: “We started off as colleagues and we became firm friends”. The two men share, he says, “an interest in politics, government and the wider world”.

He describes Mr Rosenfield as “a real mensch, a good friend who has been supportive of me when I’ve had difficult times, he’s been firm in his friendship”.

He says his friend is “super bright, he has immense integrity and a real strength of character. This job is one of almost unique pressure. There is no crisis that he’s not going to have to deal with. But he is supremely well qualified for the role”.

After 10 years at the Treasury Mr Rosenfield went first to Bank of America/Merrill Lynch, and latterly to Hakluyt, a strategic advisory firm founded by former officials of MI6, the secret intelligence service. Hakluyt’s chair is Lord (Paul) Deighton, with whom Mr Rosenfield worked at the Treasury, particularly during the structuring of the budget for the 2012 Olympics. It is understood that it was Lord Deighton who recommended Mr Rosenfield for the Downing Street post.

Lord Finkelstein first encountered Mr Rosenfield when the latter was working for Chancellor George Osborne, with whom the Conservative peer was good friends. He said: “I met Dan a fair amount professionally, for the first time in 2010. We’re both big football fans, we always have that in common. He’s got a good sense of humour — George has got quite a cynical sense of humour, so a lot of laughing went on and Dan was very much part of that. He was liked by the team and we all thought it was a good choice [for him to go to Number 10]”.

He believed Mr Rosenfield “has all the attributes necessary to do this job: understanding politics and the system, being a nice, civilised human being but also someone who is tough, firm, and can tell your boss the truth — which I know that he does, because I’ve seen him do it. He doesn’t duck difficult decisions, and he doesn’t confuse being nice with being weak”.

But Lord Finkelstein warned: “Boris Johnson is not George Osborne or Alistair Darling. He will need different parts [of Mr Rosenfield], the bit of him that is a frank truth-teller and will introduce discipline into the process”.

Away from Whitehall, Mr Rosenfield — who is a keen cyclist and has passed on his love of sports to his children, Rafi, Natasha and Benjamin — is an engaged chairman of World Jewish Relief, a role he has held since 2016. Paul Anticoni, the charity’s chief executive, says: “Dan has been, and continues to be, an outstanding chair of World Jewish Relief. Proud of our heritage, he has led the organisation to deliver better services to more people both at home and abroad during his tenure. Last year we touched the lives of 72,000 people. He has shown great empathy with our older Jewish clientele in Eastern Europe, the plight of refugees, particularly those given the right to settle in the UK, and victims of disaster worldwide. He has celebrated World Jewish Relief’s Jewish identity in assisting those both within and beyond the Jewish community”.

Henry Grunwald QC, WJR president, said: “He has been a fantastic chair, as was his predecessor, James Libson”. He said Mr Rosenfield brought the qualities of “common sense, person-to-person skills, first-rate management skills”, to the role, which he judged would work well in Downing Street, too.

Though Mr Rosenfield was due to remain chair of WJR until October 2021, it is now understood that he is likely to stand down after the charity’s “virtual dinner” at the beginning of February next year. Most observers believe the demands of the Downing Street job would, in any case, make it difficult for Mr Rosenfield to continue as WJR chair.

As chair of WJR, Mr Rosenfield had a seat on the Jewish Leadership Council. Its chair, Jonathan Goldstein, said: “I have enjoyed working with Dan during his time as a JLC council member. He is thoughtful, smart and an all-round nice guy”. He was “solid, considered, with a wonderful demeanour. He should be proud of getting this job — and we should be proud, too. [The appointment] is a wonderful honour for the community.”