The new PM will depend on Whitehall for survival—whether he knows it yet or not

Britain’s new prime minister will be clapped into No 10 by the staff only hours after they have clapped out Theresa May. The ritual can be emotional. As a centre of government, 10 Downing Street is small and everyone knows everyone else from the highest to the lowest. There is a family atmosphere, for it is a home as well as a political nerve centre, with the PM living in a flat upstairs and Larry the cat curled up in the window of the front hall. There is fellow feeling for a premier who leaves in difficult circumstances—sometimes tears.

In a professional sense, many of the 200 or so staff in No 10—the messengers, the police, the secretaries—will be largely unaffected by the arrival of a new PM. Not so the cadre of top officials, led by Cabinet Secretary Mark Sedwill, who will greet the new prime minister in the chequered hall and lead him to the cabinet room. Their task is to choreograph all aspects of the changeover. Ever since 19th-century reforms replaced patronage with merit in Whitehall, the proud boast of these mandarins has been that they, too, can work seamlessly through every transition, because politicians of all stripes can trust them.

Yet as with so many of our constitutional arrangements, the question is whether Brexit will test convention to breaking point. With politicians bitterly divided and the government limping along with the tiniest majority, this is set to be the most difficult transition the civil service has ever faced in peacetime.

No matter how radical the policy changes under a new PM, the tradition has been that there are not radical changes in the personnel of the permanent civil service. No prime minister, for example, has ever sacked a cabinet secretary since the role was created for Maurice Hankey a century ago. But since the Brexit vote, politicians have been tugging away at the convention. Figures on both the right and the left have attacked named civil servants. Consider Olly Robbins, May’s chief Brexit adviser who became the whipping boy of hardline Brexiteers for his role in crafting her deeply unpopular withdrawal deal. That episode does not fill senior civi servants with confidence. Even more significantly, some Boris Johnson supporters have been manoeuvring to have Sedwill replaced.

To remove him would undermine the civil service principle of impartiality and two former cabinet secretaries were moved to write to the Times condemning any such plan. The rows that flared up over unnamed officials saying Jeremy Corbyn was too frail to govern and—more seriously—over the leaking of high-level diplomatic cables critical of President Trump, was another reminder of how Whitehall is struggling to keep itself above the fray in our polarised times. One factor in the resignation of ambassador Kim Darroch was Johnson’s craven failure to back him publicly on TV the night before.

And yet, it has often been a mistake to bet against the mandarins. They are, after all, the ones who will be on hand to guide the new leader through the critical decisions that have to be faced from day one.

One crucial choice facing the new prime minister will be... where to sit. Will he go for the cabinet room, next door to the civil service private office? Or the nearby den, where Tony Blair conducted sofa government? Perhaps he’ll prefer the privacy of the study upstairs or, like Gordon Brown, opt for an open plan arrangement on the other side of the connecting doors to No 12. It matters, too, where everyone else sits. In his forthcoming book No 10: The Geography of Power at Downing Street, Jack Brown of King’s College London says the “scramble for a seat as close as possible to the PM is a common theme” in advisers’ and officials’ memoirs. A premier bent on putting the mandarins in their place, and maybe even out in the cold, could seat his political appointees close, where they can act as gatekeepers, like May’s “gruesome twosome” Nick Timothy and Fiona Hill.

But Catherine Haddon of the Institute for Government has detailed the tsunami of tasks which will immediately arise, where professional advice might be handy. First the prime minister will have to take calls from world leaders—Barack Obama was on the phone within half an hour of Cameron arriving in No 10. He’ll need to call the UK’s other national leaders, most importantly the DUP’s Arlene Foster. Will she continue to prop up the government? There will be the cabinet reshuffle to organise. Barmy though it is, everyone expects the first appointments to be announced within 24 hours. These don’t always go according to plan, with furious reactions along the lines of: “Leader of the House? I expected Chancellor!”

One key job for Whitehall will have been writing policy briefs for the new boss. With Jeremy Hunt and Johnson prepared to crash out of the EU without a deal, giving advice will require finesse. Officials are duty bound to speak truth, but it will be tempting to win the PM’s confidence by pulling punches. Johnson reportedly covered his ears and hummed the national anthem when given unwelcome advice at the Foreign Office.

Squandering the independence of Whitehall would be ruinous. But as attacks on the civil service mount, don’t panic just yet. Nothing prepares you for being prime minister, so there is little choice but to rely on the advice of officials who will have game-planned for all eventualities. And if Whitehall can help the new PM chart a way through the great Brexit snarl up, its authority and prestige could even be enhanced.