Tony Blair was to wade into the British general election campaign on Tuesday, with the former prime minister set to sound a warning about the dangers of leaving the EU.

Blair, who was in office from 1997 to 2007, is to claim Prime Minister David Cameron’s planned referendum on European Union membership threatens the British economy.

Conservative centre-right leader Cameron, if he remains prime minister after the May 7 election, has pledged to renegotiate Britain’s relationship with the EU and then hold an in-or-out referendum on the outcome by the end of 2017.

Blair was to speak in his former Sedgefield constituency in northeast England, in a first campaign stop this week in support of the main opposition centre-left Labour Party, which he headed for 13 years and led to three general election victories.

The possibility of leaving the EU would create job insecurity and leave a “pall of unpredictability hanging over the British economy“, Blair was to say, according to pre-released extracts from his speech.

“I believe passionately that leaving Europe would leave Britain diminished in the world, do significant damage to our economy and, less obviously but just as important to our future, would go against the very qualities and ambitions that mark us out still as a great global nation.” He claimed Cameron’s plan was a “concession” to the right of his party, a “manoeuvre” to win back voters from the anti-EU UK Independence Party and “a sop to the rampant anti-Europe feeling of parts of the media.

“This issue, touching as it does the country’s future, is too important to be traded like this.” Blair was to set the issue in the strategic context of an aggressive Russia and the economic rise of China and India.

“Do we really think this is the time in which to put into play our very membership of the European Union, the largest commercial market and most developed political union in the world? And the one on our doorstep?” he was to ask.

The 61-year-old Middle East peace envoy also voiced support for Labour leader Ed Miliband, who has tried to distance himself from the Blair era and junked Blair’s “New Labour” approach.

“He is his own man, with his own convictions and determined to follow them even when they go against the tide,” Blair was to say.

“I want Labour, under Ed’s leadership, to be the government of our country on May 8. I believe we can and will do it.” Psephologists predict a hung parliament. The latest BBC poll of polls puts the Conservatives on 34%, Labour on 33% and UKIP on 13%.