So you're the new Prime Minister – what next?

There are a few traditions in UK changes of prime minister. On Wednesday, after she returns from her meeting with the Queen at Buckingham Palace, Theresa May will head straight into Number 10 to make a speech in front of that famous front door. Then, having clapped David Cameron out the door, officials will be lined up to applaud May as she enters. Before she can begin the business of running the country, however, there are five urgent items on May’s to-do list:

1. After a few words on the doorstep, May will see Sir Jeremy Heywood, the Cabinet Secretary, and her other key officials. Heywood will have a well-worn checklist used by his predecessors for incoming PMs, which outlines the various constitutional and official roles that the new PM will be taking over.

2. May will then be briefed on security and defence. As a former Home Secretary and member of the National Security Council, she will be very familiar with the heads of agencies and military chiefs, but she won’t have experienced the full briefing on UK nuclear deterrence. She will appoint two nuclear ‘deputies’, two other members of her Cabinet, who would take any decision on nuclear release in the event of her incapacity. She will also be asked to immediately hand-write letters of last resort to the commanders of the four UK Trident submarines on what action they should take if the UK suffered a catastrophic nuclear attack. Tony Blair reportedly went quite pale when this role was starkly set out.

3. There will also be a briefing on ‘business requiring immediate attention’ that will cover which prime ministerial engagements she wants to take on (her first chance to take the stage with other world leaders will likely be at the September G20 summit in China). One of the things that takes incoming PMs by surprise is the amount of time eaten up by foreign affairs – phone calls from heads of state could easily fill much of the next two days.

4. Then she moves to her first big public task: forming her new Cabinet. Chancellor, Foreign Secretary and Home Secretary are usually done swiftly. There will be lots of focus on the balance between Leave and Remain ministers. One of the biggest appointments will be the person who will be in overall charge of the Brexit negotiations. She will also want to think through the options for supporting that minister and herself through the Brexit negotiations.

5. Finally, she will want to put her own stamp on Downing Street. May will need to decide whether to keep a political chief of staff and what sort of press operation she wants. She will also need to appoint a new Policy Unit head and political secretary to help manage the party. When he moved over from HM Treasury, John Major’s first key appointments included replacing Bernard Ingham with Gus O’Donnell as Treasury Press Secretary, and then appointing Sarah Hogg to run his Policy Unit.

In Number 10, May will have a lot of seasoned officials to fall back on – and her experience as a Cabinet Minister will count for much. But over time she will need to establish her own working routines. Cameron had twice-daily strategy meetings at 8.30am and 4.00pm, often chaired by the Chancellor – that exceptional arrangement is unlikely to persist. But there is one feature that we can count on sticking around: Larry the cat. As various press reports have assured us today, he will remain in post to welcome in the new PM.