A decision to leave the European Union would make the UK "less attractive" to Japanese investors, Shinzo Abe, the country’s premier, has warned in a visit to Downing Street.

In another major international intervention in the referendum campaign, Mr Abe stressed that Japanese firms viewed the UK as a "gateway" to Europe.

At a joint press conference with Prime Minister David Cameron in No 10, Japan’s Prime Minister said a Leave vote "would make the UK less attractive as a destination for Japanese investment".

Mr Abe also stressed that Tokyo was more interested in doing a trade deal with the EU as a block, rather than "individual states" in Europe.

The views echoed those of US President Barack Obama, who provoked a furious backlash from the Leave camp when he warned a post-Brexit Britain would be at the "back of the queue" when it came to a new economic agreement with Washington.

The Herald: Prime Minster David Cameron welcomes US President Barack Obama to Downing Street, London, ahead of a bilateral meeting in number 10. Picture: Lauren Hurley/PA Wire

Mr Abe said the referendum was a matter for the British people but added that Tokyo "would be watching your decision with very close attention".

The Japanese premier said he wanted the UK to keep its strong voice in Europe as this gave it more influence over the international economy.

Mr Cameron and Mr Abe stressed they wanted to speed up the conclusion of a landmark trade deal between the EU and Japan.

Read more: David Cameron and Boris Johnson take EU referendum battle to Countryfile

The Japanese PM pointed out that more than 1,000 Japanese firms had invested in Britain, securing some 140,000 jobs.

"British membership,” insisted Mr Abe, “is also best for Japanese investment in the UK."

Japan's premier is also today due to have an audience with the Queen and to visit Chequers for further talks with Mr Cameron.

As the June 23 poll nears, other international leaders are expected to come out in favour of the UK remaining in the EU.

Also at the press conference, Mr Cameron appeared to offer an olive branch to Donald Trump, saying the Republican candidate "deserves our respect" for becoming the presumptive nominee in the US presidential race but refused to apologise for once having branded his remarks on Muslims "divisive, stupid and wrong".

The Herald: Prime Minister David Cameron addresses workers and activists at the Britain Stronger In Europe campaign headquarters in London, ahead a referendum on Britain's membership of the EU. Photo credit: Stefan Rousseau/PA Wire

No 10 has already indicated that the UK Government has been making diplomatic overtures to the Trump camp and the PM’s words will be seen as another attempt to smooth relations with the presidential hopeful.

Last year, Mr Cameron unleashed an attack on the outspoken billionaire businessman after he called for a ban on Muslims entering the US.

The PM said at the time: “His remarks are divisive, stupid and wrong and if he came to visit our country he'd unite us all against him."

But asked today whether he would apologise to Mr Trump, the Conservative leader replied: "I have to say that knowing the gruelling nature of the primaries and what you have to go through, anyone who makes it through that extraordinary contest to lead their party into a general election deserves our respect.

"What I said about Muslims, I won't change that view. I'm very clear that the policy idea that was put forward was wrong, is wrong and will remain wrong."

Earlier this week, George Papadopoulos, an advisor to Mr Trump, said suggested Mr Cameron should apologise for his comments, noting: “To see Mr Cameron come out as the most vocal opponent was uncalled for. Considering we believe the UK-US relationship should be a cornerstone not just of Nato policy but elsewhere it would be wise for him to reach out in a more positive manner to Mr Trump.”