Secret tunnels, nuclear codes and a blizzard of left-wing policies: GLEN OWEN, DAN HODGES and ANNA MIKHAILOVA on Starmer's first day in No.10

It ain't over till the fat lady sings, but if the polls are even close to being right, it will take the political equivalent of an asteroid obliterating the Earth to stop Sir Keir Starmer from walking through the door of No 10 on Friday.

The well-oiled machinery of the British state has been purring towards this potentially seismic moment for more than a year: Sue Gray, who spent years at the top of the Civil Service before switching to become Starmer's chief of staff, has led the transition talks – and has drawn up the grid for the first 100 days of a Labour government.

With the parliamentary recess looming at the end of July, Starmer is expected to move fast to cement his statist vision of the country's future – led by a repeal of the Rwanda migrants scheme, French-style union laws and the slamming of VAT on private school fees.

When he returns from his visit to Buckingham Palace, to ask the King for his permission to form a government, Starmer will deliver a brief speech from Downing Street, before being greeted at the door of No 10 by Cabinet Secretary Simon Case.

After being clapped through the door by staff, he will be led to the Cabinet Room to meet his most senior officials: it was at this point in 2019 that Boris Johnson started blurting out what he had discussed with the Queen, until he was hastily reminded about the protocol of sovereign discretion.

Starmer, pictured today, is expected to move fast to cement his statist vision of the country's future, led by a repeal of the Rwanda migrants scheme, French-style union laws and the slamming of VAT on private school fees

Chillingly, Starmer, whose predecessor Jeremy Corbyn vowed never to use the nuclear deterrent, will then be told by a senior naval commander to write four identical handwritten 'letters of last resort' to the Trident submarine commanders

Starmer's first task will be to listen to a detailed personal security briefing – he will be given the option of asking his wife and two children to join – covering issues such as a terrorist attack on No 10. A source said: 'The new Prime Minister is literally informed that they have to leave immediately, without argument or discussion, through a network of secret tunnels which lie under Whitehall.'

Chillingly, Starmer, whose predecessor Jeremy Corbyn vowed never to use the nuclear deterrent, will then be told by a senior naval commander to write four identical handwritten 'letters of last resort' to the Trident submarine commanders – orders which will be applied if the Government has been wiped out in a nuclear attack. An industrial-sized shredder will be wheeled in to destroy the existing letters from Rishi Sunak. David Cameron responded to this on his first day in 2010 by putting his hand on his forehead and exclaiming: 'Oh my God, this is real!'

Starmer will also have to draw up a shortlist of the most senior aides he would want to join him in a nuclear bunker – a subject of jealous in-fighting in previous regimes.

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By now, the first calls will be coming in from world leaders. A source said: 'This is regarded as very important. The first conversation sets the entire tone for the new diplomatic relationship.

'A lot of thought goes into what the first 'ask' will be to each world leader, what they will be demanding in return, and what the response will be.'

While all this is going on, Starmer will also be introduced to the duty clerks, Garden Room Girls and manager of the PM's flat – he will live 'above the shop' with his family – who will collectively manage his daily life on a minute-by-minute basis.

A government source said: 'It is quickly made clear to the new PM that these people will be running almost every aspect of his daily affairs. It's then they realise they're not just starting a new job, they're handing over their lives. It is very detailed.

'They ask what time the PM wants to be woken – do they want a call or a knock on the door, do they want to take breakfast in the flat, or something at their desk? Do they want official papers brought up, or prefer to work on them in the main building? It's stuff like that.'

Starmer's mind will then turn to the appointment of his Cabinet. While most of the senior members of his frontbench are expected to move directly into position, there is still scope for surprises: Shadow Foreign Secretary David Lammy will be particularly nervous in the wake of a whispering campaign against him generated by his virtual absence from the election campaign trail.

Gray has been in close contact with shadow Cabinet ministers during the campaign to test their readiness for government, with many called in for face-to-face meetings in her office in Labour's South London HQ and grilled on their plans for the first 100 days. Central to the discussion have been which measures to include in the King's Speech on July 17, which would set out Starmer's legislative programme.

Gray started the process in September, soon after she took up the position, when she ordered the Shadow Cabinet to be 'match fit' for their first weeks in office.

One aide said of the former Whitehall mandarin: 'She holds the pen. It's been pretty seamless. She has mostly told us to crack on with our plans, but has also suggested useful contacts to speak to about implementation and offered her own ideas.'

Likely to be the most pressing issue is immigration. Labour has promised to axe Sunak's Rwanda migrant deportation scheme 'on day one': with up to 60,000 migrants earmarked for deportation to Rwanda, they will by definition be handed an effective 'amnesty' and placed in the asylum system.

When combined with an expected increase in small-boat crossings, it could bring the Starmer honeymoon to a swift end. Shadow Home Secretary Yvette Cooper, who plans to start work on her new Border Security Command on day one, will usher in a 'national security sprint' to identify emerging threats to the UK.

Starmer will also have to draw up a shortlist of the most senior aides he would want to join him in a nuclear bunker, a subject of jealous in-fighting in previous regimes

Her other plans include laws to crack down on antisocial behaviour, improve preparedness for terrorist attacks and launch a review on violence against women.

Shadow Chancellor Rachel Reeves will start by setting a date for the next Budget; she will also legislate in the King's Speech to impose VAT on private school fees from 2025.

Angela Rayner, Labour's deputy leader, has been spearheading the party's plans to introduce new workers' rights through legislation, including an end to zero-hours contracts and easing restrictions on union activity.

Wes Streeting, the likely Health Secretary, says he will reopen negotiations with the British Medical Association to try to end the doctor strikes.

He says that his focus for the first 100 days will be Labour's pledge to add 40,000 extra NHS appointments a week, giving direction to NHS trusts, setting up surgical hubs and forcing more NHS staff to work overtime on weekends and evenings.

Starmer will take his first foreign trip as PM just four days after his appointment, attending a summit of the Nato alliance in Washington alongside Joe Biden and other world leaders. And on July 18, the Prime Minister will host major EU leaders the European Political Community summit at Winston Churchill's birthplace Blenheim Palace in Oxfordshire.

Churchill wrote about his own first day as Prime Minister in The Gathering Storm, saying: 'As I went to bed about 3am, I was conscious of a profound sense of relief . . . At last I had the authority to give directions over the whole scene.'

If the polls are correct, Starmer's own 'authority to give directions' will be almost completely untrammelled.