Photograph: (Kriss) Szkurlatowski

The leaders of some of Britain's largest trade unions on Monday made a joint appeal to their 6 million members not to vote to leave the European Union, warning that a British exit would lead to the erosion of workers' rights.

"After much debate and deliberation we believe that the social and cultural benefits of remaining in the EU far outweigh any advantages of leaving," the leaders of Unison, the GMB, Unite and seven other unions said in a letter published in The Guardian.

Prime Minister David Cameron and senior figures from three other political parties also issued a joint statement on Monday, accusing the Vote Leave campiagn of "perpetuating an economic con-trick on the British people" by failing to give a detailed economic plan for Britain outside the EU.

"It's time for the Leave campaign to outline their economic plan for Britain outside Europe," Cameron, former acting Labour leader Harriet Harman, Liberal Democrat leader Tim Farron and Green Party leader Natalie Bennett said at a Remain campaign event in London.

Cameron also criticised Vote Leave's "simply wrong" claim that Britain could be forced to contribute to bailouts of eurozone nations.

"We are not part of eurozone bailout schemes," he said. "We also have a veto over any EU budget increases."

Vote Leave was "undemocratic and reckless" by failing to outline its economic plans, Cameron said.

Most opinion polls put the Remain vote marginally ahead, but many people are still undecided and there is uncertainty about how turnout could affect the result.

In a Daily Telegraph poll of some 19,000 subscribers, 69 per cent of respondents said they plan to vote for a British EU exit, or Brexit, in the June 23 referendum.

The Telegraph readers made Cameron's fellow Conservative Boris Johnson, who heads the Vote Leave campaign, their favourite to become Britain's next prime minister.

The newspaper said Monday's comments by Cameron reflected the intensification of a "civil war" over Brexit in the Conservative Party.

The trade union leaders said British and European unions had "fought hard to secure valuable working rights legislation at EU level," including maternity and paternity rights, and equal treatment for full-time, part-time and agency workers.

"If Britain leaves the EU, we are in no doubt these protections would be under great threat," they said.

The EU's recent political direction "has taken governments down a path of austerity and liberalization," they said, promising to "help shape a Europe with a renewed social agenda and a Europe that values investment in our public services."

The Remain campaign is expected to continue to stress the economic costs of a British EU exit, or Brexit, while the Leave side is likely to increase its focus on immigration ahead of the referendum on June 23.

Cameron made the referendum a key promise in his manifesto ahead of a general election in May 2015, when the Conservatives won 330 of the 650 parliamentary seats.

He negotiated a deal earlier this year for EU reforms that would give Britain what he called a "special status."

But he is likely to come under pressure to step down if the public votes to leave the EU, and Johnson is widely seen as a leading contender to succeed him.

Latest news

Francis, first pope to visit Anglicans in Rome, weighs S Sudan trip

Pope Francis became the first leader of the Catholic Church to visit the Anglican community in Rome on Sunday, where he said he was considering a trip to famine-struck South Sudan.

Ibrahimovic lifts Man United past Southampton in League Cup final

Zlatan Ibrahimovic scored an 87th-minute winner as Manchester United beat Southampton 3-2 in an exciting League Cup final on Sunday.

London screens Iranian director's film amid Oscars boycott

Thousands of people watched a free screeening of Iranian director Asghar Farhadi's film "The Salesman" in London on Sunday to coincide with the Oscars.

Messi grabs winner as Barcelona go top with victory over Atletico

Lionel Messi scored the winner as Barcelona beat Atletico Madrid 2-1 on Sunday to move top of the Spanish first division.

Dubrovnik Sun Gardens Hotel member of The Leading Hotels of the World

The Dubrovnik Sun Gardens Hotel has joined the Leading Hotels of the World, Ltd., a global hospitality consortium of more than 375 hotels and resorts in over 75 countries.

Biggest Bosnian Serb party ceases all contact with Izetbegovic over ICJ judjment review request

The main committee of the biggest Bosnian Serb party which makes up the ruling majority in Bosnia and Herzegovina decided o Sunday that its officials would cease all contact with member of the Bosnian President Bakir Izetbegovic until the crisis occurred following the submission of a request to the International Court of justice (ICJ) to review its ruling against Serbia is resolved.

Egypt court adjourns Morsi retrial over prison escape

An Egyptian court adjourned a case against former president Mohamed Morsi until March 29 on Sunday, during the first session of his retrial over orchestrating a prison escape during the 2011 uprising.

Hamas rejects Netanyahu's proposal for international forces in Gaza

The Islamic Hamas movement rejected on Sunday Israeli Prime Minister Benjamin Netanyahu's proposal to send international forces to the Gaza Strip, the coastal enclave that Hamas has been ruling since 2007.

Deloitte: Growing optimism among CFOs

Chief financial officers (CFOs) in Croatia are more optimistic about growth and financial prospects in 2017 than they were last year, with most of them expecting increases in their company's revenue, a survey shows.

Russian agents main suspects for attempted coup in Montenegro

Russian citizens Eduard Shumakov and Vladimir Popoc, suspected of organising terrorist activities in Montenegro and forming a criminal organisation, are agents of Russia's Main Intelligence Agency (GRU), British, U.S. and other intelligence agencies confirmed, the Podgorica-based media reported on Sunday.

Six injured, 96 detained in Berlin fan clashes

Six people were treated in hospital and 96 detained in clashes in Berlin between fans of Hertha Berlin and Eintracht Frankfurt, police said Sunday.

Croatian government condemns extremism

The Croatian government on Sunday condemned all forms of extremism and acts of provocative nature aimed against the Serb minority in Vukovar as well as the rally organised by the Autochthonous Croatian Party of Rights (A-HSP) in Zagreb on Friday.