On 9 September, Simon Case will become the 13th cabinet secretary.

Another white man with an Oxbridge degree. Another career civil servant, experienced in policy but not delivery. Another whose rise started with a posting to the private office of another prime minister, David Cameron. The only thing that stands out about Simon Case is his youth – at 41, he is younger than all other cabinet secretaries since the first. He would have been on the insiders’ watchlist as a potential cabinet secretary – but perhaps not yet.

His appointment follows a pattern established by this government: of removing permanent secretaries but then choosing another highly conventional appointee to fill the vacancy. Matthew Rycroft, permanent secretary at the Department for International Development, glided over to fill the gap created by Philip Rutnam v Priti Patel, when the home secretary’s top official noisily quit; Philip Barton, high commissioner in Delhi, is taking over the task of welding together the Foreign Office and Department for International Development for Dominic Raab now Simon McDonald has been told that his diplomatic services are no longer required; Case will replace ousted cabinet secretary Mark Sedwill when he moves off to the red benches of the Lords.

This is clearly a personal choice of Boris Johnson – but it is not a political appointment. Case, we are told, had to be press-ganged into service and persuaded to stay in Whitehall rather than return to Kensington Palace, where he had served as private secretary to Prince William. It is not yet clear whether he went through the competition launched in July or whether he was asked to step in when other candidates came up short – but his appointment comes with the blessing of the civil service commission. Unlike others, he had not allowed “friends” to speculate about his Brexit credentials to curry favour with the prime minister.

It is hardly surprising in current circumstances that no former permanent secretary was tempted, despite rumours that a former Whitehall big-hitter might make a comeback. So no Dame Sharon White, Dame Nemat Shafik or Sir Suma Chakrabarti. Many of the more promising internal candidates shied away from reaching out for what looks like a poisoned chalice. The door is now firmly shut on the route established from Treasury permanent secretary to cabinet secretary.

The biggest thing going for Case is that he is the prime minister’s choice. Johnson has seen him in action – he was drafted into Downing Street to help tackle the coronavirus pandemic. He has the prime minister’s trust. Moreover, he can rest more secure than most top civil servants: losing two cabinet secretaries would look careless indeed.

But he faces challenging times. He still has to help steer the government through a Covid winter. The government still has to get test and trace working well; its quarantine policy is fraught with absurdities; local lockdowns look too ad hoc; schools may be going back, but there are big rocks in the road ahead.

Meanwhile he needs to deal with Brexit. Whether it’s deal or no deal, there is a hard rain coming for many UK businesses. So far the Cabinet Office-funded publicity campaign is lauding the opportunities of Britain’s new start, and trumpeting “growing the customs sector”. At some point he will need to tell ministers they need to start sounding the alarm, or Britain will be unconscionably unprepared for what is to come.

Most critically, the government faces major economic challenges. One is how to mitigate the impact of rising unemployment. Another is how much to spend shoring up the already fraying public services in the massively overdue spending review. The third is when and how to start rebuilding the public finances in case interest rates start to rise. The centrality of economic issues was one reason that time in the Treasury was regarded as essential preparation for the role of cabinet secretary. It’s the biggest omission on Case’s CV. This may make it harder for him to defuse the inevitable No 10/No 11 tensions that have started to emerge and will get more intense in the runup to the autumn budget and beyond.

The biggest test he will face is in convincing a battered permanent secretary class and those who work for them that he will stand up for the integrity of the civil service. Case will need to support the right – indeed the duty – of his colleagues to challenge their ministers without fearing for their jobs, while at the same time championing effective civil service reform. He will need to show too that he can hold the line on the boring niceties of conventions about appropriate use of public money and office when faced with a determined campaign team that thinks rules are for wimps.

Case starts his job in a strong position in a weakened civil service. His objective should be to leave it – and the country – strengthened.

• Jill Rutter is senior research fellow at UK in a Changing Europe