Media playback is unsupported on your device Media caption Colonel Richard Kemp explains why Veterans for Britain wants the UK to leave the EU

EU policies are undermining the UK's combat effectiveness, a dozen former senior military officers have warned.

Speaking out in favour of Britain leaving the EU, they said that Nato, and not the EU, should remain the cornerstone of Europe's defence.

Among the group is General Sir Michael Rose, whose name was originally on a letter organised by Downing Street supporting UK membership of the EU.

The Remain campaign says membership of the EU and Nato is not contradictory.

Meanwhile 300 historians - including Simon Schama, Ian Kershaw and Niall Ferguson - have signed a letter saying the UK has had an "irreplaceable role to play in Europe" in the past and must not "cast itself adrift" in the future.

In other developments in the EU referendum campaign:

The Institute for Fiscal Studies is warning that leaving the EU could extend austerity by two years

It says an EU exit could save up to £8bn a year but this may be outweighed by the resultant fall in national income

The Vote Leave campaign is to focus on immigration in an attempt to appeal to its core voters

Ex-PM Gordon Brown is to address the European Parliament about the case for EU membership

Chancellor George Osborne is to stand in for David Cameron at PMQs

Follow the latest news on the BBC's EU referendum live page

There has already been a series of letters from UK, US and Nato commanders urging Britain to remain in the EU - or risk losing influence.

Now Veterans for Britain, a campaign group set up by serving and former military personnel, is making the case for Britain to leave.

The former senior military commanders - including Falklands veteran Major General Julian Thompson, former deputy chief of the defence staff Sir Jeremy Blackham and Lieutenant General Jonathon Riley, who commanded coalition forces in Afghanistan - have said the UK's national interest would be best served outside the EU.

General Sir Michael Rose, a former director of special forces and a commander in Bosnia, has expressed concerns that the EU is trying to set up its own army that could undermine the Nato alliance.

Downing Street admitted it had made a mistake earlier this year when it released a letter claiming he was among former military top brass who wanted Britain - which has the fifth largest defence budget in the world - to remain in the EU.

Image caption General Sir Michael Rose has expressed concerns that the EU is trying to set up its own army

General Rose said sovereignty and defence were indivisible and that EU policy had already seriously undermined Britain's combat effectiveness.

"I believe that the UK's contribution to European defence can manifestly be better made solely through Nato than by trying to spread our limited resources too thinly, in order to include European defence and security policy initiatives into the UK's defence programme," he said.

"It is something of an insult to our European partners, in particular France and Germany, to imply that UK membership of the European Union is necessary to secure future peace in Europe."

'Gift to Putin'

In response, campaign group Britain Stronger in Europe said there was an "overwhelming consensus" among military chiefs, including four former chiefs of the defence staff, that Britain was "stronger and safer" in the EU.

And Labour MP Dan Jarvis, a former paratrooper who served in Iraq, has warned EU exit would be a "gift" to Russian President Vladimir Putin.

Meanwhile, former Labour frontbencher Tristram Hunt has called on Jeremy Corbyn to "redouble his efforts" in the campaign for Britain to remain in the EU, saying the opposition leader "should be out there every day as we go up towards the poll".