David Cameron has accused Leave campaigners of seeing lost jobs and businesses as "a price worth paying" for getting out of the EU.

He is thought to be referring to comments by Boris Johnson and others although he does not name them.

His remarks have angered Leave campaigners who have described them as unworthy of a prime minister.

Downing Street says 80% of the PM's speech focused on the positive economic advantages of EU membership.

But he also suggested that people will pay higher mortgages if the UK leaves the EU because of the pressure on the pound and interest rates.

'Do us down'

In a speech to car workers in Ellesmere Port, near Chester, Mr Cameron said people want the facts and arguments about the EU presented in a "calm and rational way".

Retaining full access to the EU's single market, he argued, enables British businesses to sell their goods, without the threat of tariffs, to 500 million people, bypass trade obstacles and be a part of the most "ambitious and comprehensive" free trade agreements with the rest of the world.

He said Leave campaigners' assurances that Britain could quickly strike favourable trade deals with the EU after exit were based on "guess work, at a time when we need facts". One fact, he suggested, was that "it takes years to strike trade deals".

"If we leave, you have to think for a moment what would be the reaction of the other 27 countries?" said the prime minister.

"Are they going to want to sign deals, including deals with us, that make sure we have the preferential access we have now? Or are they going to try and club together and make sure they look after their car plants in France and Germany and Italy and Spain - and start trying to find ways to do us down?

"They can't do that today because we are in the single market - there is a level playing field, we know we have that access."

He said the Leave campaign wanted to risk that with " a leap into the unknown".

Image caption Stephen Hawking is arguing EU grants helps the UK attract leading researchers

Mr Cameron also criticised opponents who he claims are willing to sacrifice economic prosperity for wider political goals. "For those who advocate leaving, lost jobs and a dented economy might be collateral damage, or a price worth paying. For me, they're not. They never are."

The Britain Stronger in Europe campaign has released a list of quotes from Leave campaigners it claims backs up the prime minister's point.

'More jobs'

They include Boris Johnson saying "well, it might or it might not", when asked by the BBC's Andrew Marr about whether leaving the EU would cost jobs.

But Commons leader Chris Grayling hit back at the prime minister's jobs claim in an interview with BBC Radio 4's Today programme, saying: "That is simply not true. It is about creating the opportunity for more jobs.

"European Union regulations cost jobs in this country. They increase costs for business. They make it less desirable to employ people in the UK."

In a speech on Thursday Mr Grayling - one of five cabinet ministers campaigning for Britain to leave the EU in 23 June's in-out referendum - turned his focus on to Mr Cameron's EU reform deal claiming it could leave Britain in a "worse situation".

In other EU referendum developments on Thursday the editor of the Sun stood by its claim on Wednesday that the Queen backed "Brexit" - a headline which prompted Buckingham Palace to make a formal complaint to regulator Ipsos.

And Professor Stephen Hawking and 150 fellows of the Royal Society, including three Nobel laureates and the Astronomer Royal, warned in a letter to the Times, that leaving the EU could severely affect research in Britain.