Sir Keir Starmer has said he will have to take “tough decisions” when asked about tax hikes as he vowed to approach challenges with a “raw honesty”.

Facing his first media grilling as Prime Minister on his first full day in Downing Street, he also said the Tories’ Rwanda deportation plan was “dead and buried”.

The landslide victory in the General Election has given Labour “a clear mandate to govern for all four corners of the United Kingdom,” Sir Keir said as he set out plans to tour all four UK nations.

The new Government faces difficult choices over the public finances, with official forecasts implying major spending cuts over the coming years.

During the election campaign, Sir Keir insisted he had no plans for major tax increases.

Asked on Saturday whether he would be willing to raise levies to fund public services, the Prime Minister told journalists: “In relation to the tough decisions, we’re going to have to take them and take them early. And we will do that with a raw honesty.

“But that is not a sort of prelude to saying there’s some tax decision that we didn’t speak about before that we’re going to announce now.

“It’s about the tough decisions to fix the problem and being honest about what they are.”

Sir Keir also said:

– The previous government’s controversial plan to send migrants to Rwanda was a “gimmick” which was “dead and buried before it started”.

– He would chair cross-departmental “mission delivery boards” to “put into action the plans that we have set out in our manifesto”.

– It was “impossible” to say the Government would stop the early release of prisoners, saying overcrowding was a “monumental failure of the last government” and “we can’t fix it overnight”.

– He would hold a meeting of the metro mayors on Tuesday to discuss “their part in delivering the growth that we need” across the UK. This would include non-Labour mayors because “regardless of the colour of their rosette, my door is open and my Government will work with them”.

– The Government has already started to work on fixing the “broken” NHS, and that the effort to get 40,000 extra appointments a week up and running as pledged “starts straight away”.

After sweeping to a historic victory at the polls, Sir Keir said his party had received “a mandate to do politics differently”.

“This will be a politics and a Government that is about delivery, is about service. Self-interest is yesterday’s politics.”

Sir Keir also said: “We clearly on Thursday got a mandate from all four nations.

“For the first time in 20-plus years, we have a majority in England, in Scotland and in Wales.

“And that is a clear mandate to govern for all four corners of the United Kingdom.”

He set out plans to travel to Scotland, Northern Ireland and Wales, before returning to England, during which time he would meet First Ministers and “establish a way of working across the United Kingdom that will be different and better to the way of working that we’ve had in recent years and to recognise the contributions of all four nations”.

He is expected to meet Scotland’s First Minister John Swinney on Sunday and then visit Stormont and Cardiff on Monday.

Labour did not field any candidates in Northern Ireland in the election.

Sir Keir’s party won 412 seats and the Tories 121, marking the worst result in Conservative history.

Answering questions from reporters, he said: “I am restless for change and I think and hope that what you’ve already seen demonstrates that.”

“We have been planning for months to hit the ground running,” he said, adding: “But look, it is not an overnight exercise changing the country.”

Sir Keir Starmer's new Cabinet sitting around the Cabinet table in Downing Street
Prime Minister Sir Keir Starmer hosted his first Cabinet meeting at 10 Downing Street on Saturday (Chris Eades/The Sun/PA)

The news conference on Saturday came after he chaired the first meeting of his new Cabinet, which largely mirrors his shadow team before the election.

He said he had told his ministers “exactly what I expect of them in terms of standards, delivery, and the trust that the country has put in them”.

Sir Keir will make his debut on the international stage as Britain’s premier when he flies to Washington DC for the Nato gathering next week, which is expected to include discussions on support for Ukraine.

He told the news conference: “It is for me to be absolutely clear that the first duty of my Government is security and defence, to make clear our unshakable support of Nato.

“And of course to reiterate, as I did to President Zelensky yesterday, the support that we will have in this country and with our allies towards Ukraine.”

The Prime Minister, who continues to receive calls from world leaders, will also host the European Political Community summit in the UK on July 18.