David Cameron invokes UK war dead as he makes case for EU as guardian of peace

'Whenever we turn our back on Europe, sooner or later we come to regret it,' PM says - in major escalation of rhetoric

Pulling out of the EU would usher in an era of British isolationism that would be a betrayal of our history and against our fundamental future national interest, David Cameron has warned.

In what was billed as his most emotive speech so far making the case for Britain remaining in Europe, the Prime Minister evoked the image of “rows of white headstones in lovingly-tended Commonwealth war cemeteries” as evidence of the “price this country has paid” to ensure peace and order in the continent.

And he warned that throughout British history, whenever “we turn our back on Europe, sooner or later we come to regret it”.

“Either we influence Europe, or it influences us,” he said.

“And if things go wrong in Europe, let’s not pretend we can be immune from the consequences.”

Senior Government strategists said the speech was a deliberate attempt by Mr Cameron to “move the remain campaign up a gear” and move the focus away from the economy and on to other areas which they believe will swing support behind a stay vote.

However, Boris Johnson was due to take on the Prime Minister's argument in a speech of his own, before embarking on a nationwide bus tour to make the case for leaving.

Addressing the supporters of Brexit, Mr Cameron said that throughout history British affairs have been intertwined with the affairs of Europe for “good or ill”.

And he argued that a move to leave the EU now would make the continent and the world an inherently less stable place.

“Can we be so sure that peace and stability on our continent are assured beyond any shadow of doubt?” he asked.

“I would never be so rash as to make that assumption.

“It’s barely been 20 years since war in the Balkans and genocide in Srebrenica. In the last few years, we have seen tanks rolling into Georgia and Ukraine.

“The European Union has helped reconcile countries which were at each others’ throats for decades.

“Britain has a fundamental national interest in maintaining common purpose in Europe to avoid future conflict between European countries.”

Meanwhile, the Leave campaign was embroiled in a row with a number of prominent businessmen after Michael Gove claimed that Britain would be able to leave the single market and still be able to access European trade on the same terms as present.

Mr Gove told the BBC the UK could enjoy a relationship with the EU that had “all the advantages” but “none of the pay-outs” by forging a new trade deal.

The Justice Secretary added the UK should leave the single market but would be able to agree to tariff-free trading with the remaining EU members.

But Jeurgen Maier, Chief Executive of Siemens UK, which employs 13,000 British workers and has an annual turnover of £5 billion, dismissed Mr Gove's plan as “unbelievable”.

He said: “This lacks any understanding of what the single market is all about and the benefits it generates. Unbelievable.”

He was backed by Sir Michael Rake, chairman of BT, who said the single market was “critical to the economic security of the country, investment and jobs”.

“This kind of statement moves the Leave campaign from the naive to the irresponsible,” he said.

“It proves that they have lost the economic argument and simply don't care about the very serious risks to jobs, investment and Britain's economy that leaving Europe would pose.”

Mr Gove was also attacked by Chancellor George Osborne.

“We've just had the Leave campaign admit this morning that Britain would leave the single market, that's the largest free trade area in the world,” the Chancellor said.

“That would be catastrophic for people's jobs and their incomes and their livelihoods.

”Some people might think wrecking the economy is a price worth paying, I absolutely reject that.“

Highlighting Treasury claims that families would be £4,300 worse off if the UK pulls out of the union, Mr Osborne told ITV's Peston On Sunday: ”If we leave the single market actually our analysis says we'll be worse off than that.

“And there's a short-term hit - I think it's very important for people to think about that and we are going to be producing some more research on that in the coming weeks.

”It's already clear from the Treasury analysis that for example, there would a significant shock to the housing market, that would hit the value of people's homes, that would hit the cost of mortgages.”

But Mr Gove earlier told the Marr programme that a vote to remain in the EU would leave the UK at risk of losing even more control over its financial affairs while a vote to leave would allow the country to “dictate the terms in Britain's economic interests“.

Michael Gove delivers a speech on the EU in London, Britain, 19 April 2016 (EPA)

”We should be outside the single market, we should have access to the single market but we should not be governed by the rules that the European Court of Justice imposes on us which cost business and restrict freedom,“ he said.

”At the moment there are no tariffs between the UK and other countries in the European Union. Why should we seek to impose those tariffs when we are outside?“

Mr Gove said both sides could accept there was no need to create tariffs where none existed.

"German car manufacturers are not going to want to have tariffs erected when they sell many more cars to us than we sell to them,“ he said.

"I cannot imagine a situation where, if any individual nation within the EU wanted to erect tariffs that others would let them."