Boris Johnson said he would both cut taxes and increase spending on schools as he launched his campaign to become prime minister.

The former foreign secretary has pledged to “significantly” increase the amount spent on every secondary school pupil to at least £5,000 if he wins the race to succeed Theresa May.

His leadership launch came as Cabinet minister James Brokenshire called for outsiders in Conservative leadership contest to stand aside, warning that the party did not have “the luxury of weeks of navel-gazing” as the current 13-strong field is whittled down to a final two.

Mr Johnson’s campaign launch was clearly aimed at showing Tory MPs that he is the candidate most likely to secure them a general election victory, with carefully chosen footage of the former mayor of London on voters’ doorsteps.

On Brexit, he said: “If I get in, we’ll come out, deal or no deal, on October 31.”

As well as extra funding for schools, Mr Johnson said “we need more police out there”.

He suggested he could “cut some taxes and you get more money in” to pay for his campaign pledges.

“If there is one message in that referendum of 2016, it is that too many people feel left behind, that they are not able to take part fully in the opportunities and success of our country,” Mr Johnson said.

“That’s why now is the time to unite our society and unite our country.

“To build the infrastructure, to invest in education, to improve our environment and support our fantastic NHS.

“To lift everyone in our country – and of course, also, to make sure that we support our wealth creators and the businesses that make that investment possible.

“Now is the time for us to believe in ourselves and what we can do.”

He also used his regular Daily Telegraph column to claim there is a “yawning funding gap” between schools in different areas of the country, with per-pupil funding in some parts of London at £6,800 while in other parts of the country it is £4,200.

“I pledge significantly to improve the level of per-pupil funding so that thousands of schools get much more per pupil – and to protect that funding in real terms.”

It is understood that Mr Johnson would like every secondary school in England to spend at least £5,000 per pupil.

The number of MPs vying to replace Mrs May reached 13 on Sunday, with former minister Sam Gyimah throwing his hat in the ring.

Communities Secretary Mr Brokenshire used a speech in London to urge those with little chance of winning the race to consider dropping out to speed up the process of selecting the next Tory leader and prime minister.

“We simply do not have the luxury of weeks of navel-gazing or days and days of whittling candidates down to the final two and talking to ourselves,” he said.

“At a time when the country is looking to us for leadership, we need to show this as a party.

“So, I say gently to some of my colleagues who have put themselves forward for what has been described as the Grand National of political contests: please think carefully.

“If you already know it’s going to be a bit of a struggle to get over the first fence let alone Becher’s Brook ahead, then maybe you should pull up.”

David Hughes is Press Association Political Editor.