Tony Blair is back with a dire warning about David Cameron

David Cameron’s European policy risks triggering the “most intense period of instability” in Britain since the Second World War, Tony Blair will warn on Tuesday.

This could jeopardise jobs, prosperity and the country’s influence in the world, he will add.

In his first intervention in the election campaign, the former Labour Prime Minister will use the starkest language yet to condemn Mr Cameron’s “sop” to the right of his party and parts of the media by offering an unpredictable in/out referendum of Britain’s membership of the EU.

“The oddest thing of all about David Cameron’s position [is the] Prime Minister doesn’t really believe we should leave Europe; not even the Europe as it is today,” he will say, in a speech in his former constituency in Sedgefield, Co Durham. “This was a concession to party, a manoeuvre to access some of the Ukip vote, a sop to the rampant anti-Europe feeling of parts of the media.”

Labour hopes his comments will resonate with “soft” Tory voters who supported Labour under the former PM, but feel it has moved too far to the left under Mr Miliband. By picking on Europe – an issue on which both Mr Blair and Mr Miliband agree – strategists hope to reinforce the message that greatest danger to Britain’s economic prosperity lies with the Conservatives, not Labour.

Mr Blair will warn that if the Tories are successful in May, it could not be guaranteed that a referendum would be won by pro-Europeans – and the mere fact of holding it would cause significant uncertainty to business. “The Tory campaign talks of chaos should Labour win. Think of the chaos produced by the possibility, never mind the reality, of Britain quitting Europe,” he will say. “Jobs that are secure suddenly insecure; investment decisions postponed or cancelled; a pall of unpredictability hanging over the British economy.”

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