Sir Keir Starmer has vowed to “hit the ground running” as soon as he enters Downing Street.

His first 100 days in office after the General Election will set the tone for the new Labour government.

Here the PA news agency looks at some of the key moments of the first three-and-a-bit months.

– July 5: Taking the reins

Changes of government occur at dizzying speed. After the election results return the winner overnight, the victorious party enters No 10 the following morning.

After Rishi Sunak tenders his resignation in an audience with the King, Sir Keir will visit Buckingham Palace to be formally appointed and asked to form an administration.

Sir Keir will then address the nation for the first time as prime minister from Downing Street, before meeting No 10 staff, being briefed by civil servants and starting to form his government.

Calls from world leaders flood in, potentially providing opportunities for constructive dialogue.

Legislative priorities and the timing of any major policy announcements will need to be worked out.

Sir Keir’s chief of staff Sue Gray, a Whitehall veteran, will likely be involved in decisions about how the centre of government will be structured.

Cross-departmental “mission boards” are expected to be created to make progress on Labour’s key pledges – economic growth, the NHS, crime and justice, clean energy and improving opportunity.

– Immediate priorities

There are several policy changes Labour could make within days.

One is on Mr Sunak’s stalled multimillion-pound Rwanda deportation scheme, which Labour has said it would axe on “day one”.

Labour will instead launch a new border security command, appoint “hundreds of new specialist investigators” and “use counter-terror powers to smash criminal boat gangs” in a bid to curb Channel crossings.

Kickstarting homebuilding is a top priority for the party, with Sir Keir hinting about at least three announcements in the first few weeks.

This could include plans to restore top-down targets for housing delivery in every council area in England, to allow parts of the green belt to be developed, and to recruit hundreds more planning officers.

Wes Streeting, the incoming health secretary, has vowed to make his first call to junior doctors’ leaders on the day after the election to try to end long-running strikes over pay in England.

The de facto ban on onshore wind farms could be reversed within weeks, and a year-long strategic defence review of the UK’s military capabilities launched.

Labour has also said Sir Keir’s first steps include restoring economic stability and cutting NHS waiting lists.

Other immediate issues the new government may have to confront include prisons, amid fears jails could run out of space within days, and public sector pay recommendations.

– July 9: Swearing in

The new Parliament will be summoned to meet, the Commons Speaker elected and MPs’ swearing-in could begin.

Congratulating the Speaker will be Sir Keir’s first opportunity to speak at the despatch box as prime minister, and he will likely offer some rhetoric on the future.

– July 10-11: Stepping onto the world stage

Just days after his appointment, Sir Keir will be propelled onto the international stage, jetting to Washington DC for the Nato leaders’ summit, where discussions will include support for Ukraine.

The Labour leader may hold bilateral meetings with Ukraine’s Volodymyr Zelensky and US President Joe Biden.

– July 17: King’s Speech

The monarch will open the new parliamentary session and deliver the King’s Speech setting out the government’s legislative programme.

Labour is expected to legislate to establish the centrepiece of its green energy plans – Great British Energy, a new publicly-owned company that will invest in renewables and nuclear projects.

The speech is also expected to include legislation empowering the Office for Budget Responsibility to publish forecasts of any major tax and spending changes, after Liz Truss’s ill-fated mini-budget came without projections from the fiscal watchdog.

Other new laws could be to strengthen workers’ rights, crack down on antisocial behaviour through a crime and policing bill, gradually nationalise the railways, set up a new parliamentary ethics and integrity commission, and reform the planning system and the current mental health legislation.

Labour has also indicated it will resurrect some pieces of legislation Mr Sunak promised but failed to enact before he called the election, including plans for a smoking ban for under-15s and to end no-fault evictions.

– July 18: Diplomacy abounds

After the Nato summit, Sir Keir will have another opportunity to flex his diplomatic muscles as he hosts a gathering of the European Political Community, the body that brings all 27 EU member countries together with 20 others from outside the bloc.

He will welcome around 50 heads of government to Blenheim Palace in Oxfordshire, giving him a chance to set the tone for his government’s approach to the UK’s relationship with the EU.

While Labour has ruled out rejoining the single market or customs union, the party is seeking improved trade ties with the bloc.

Sir Keir is also aiming to deepen co-operation by signing a new UK-EU security pact.

– August: Summer break and peerages

Before Mr Sunak called the election, summer recess was scheduled to start on July 23.

However, this would not have left enough time for the usual six sitting days to debate the King’s Speech and Sir Keir is expected to cut short MPs’ customary six-week summer break so that it only covers August.

Labour could create a number of new peers to bolster the party’s representation in the House of Lords and help push through its legislative programme.

– September: Conference season

The month will be dominated by party conferences, with Labour gathering in Liverpool from September 22-25 for its first conference while in power for many years.

The Liberal Democrats will meet in Brighton from September 14-17, and the Tories in Birmingham from September 29 to October 2.

– September/October: Budget

Rachel Reeves’s first key test as chancellor will be delivering her first budget, expected in September or October.

It comes as the party faces tough choices over the public finances. Official forecasts imply major spending cuts, but Labour is gambling on economic growth generating the tax receipts to avoid a return to austerity.

The autumn statement will include measures detailed in Labour’s manifesto, such as higher taxes on non-doms, scrapping the VAT exemption on private school fees and extending the windfall tax on energy companies.

Labour has ruled out raising income tax, national insurance and VAT and aims to keep corporation tax capped at 25%.

All eyes will be on whether Ms Reeves raises levies in other areas to avoid a spending squeeze on departments with unprotected budgets, which oversee services such as prisons, courts and councils, baked in by Mr Sunak’s Government.

The next spending review to set departmental budgets is expected by the end of autumn.