John Major 2008
Former British Prime Minister John Major will step into the Brexit debate by warning the Leave campaign is morphing into UKIP. Jo Yong-Hak/Reuters

The former prime minister Sir John Major will enter the Brexit debate for the first time when he will lambaste anti-EU campaigners as turning into UKIP with their emphasis on immigration.

He will tell the Oxford Union on Friday, 13 May, that the anti-EU camp has crossed the line, adding "As the 'leave' arguments implode one by one, some of the Brexit leaders morph into Ukip, and turn to their default position: immigration.

"This is their trump card. I urge them to take care. This is dangerous territory that, if handled carelessly, can open up long-term divisions in our society," he will say.

His first intervention in the debate comes after vociferous newspaper headlines were sparked by claims from the Office for National Statistics (ONS) that there were a million more long-term immigrants from the EU than recorded in official statistics. However this did not take into account short-term migration.

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Major, who is vehemently pro-EU, will make a thinly-veiled criticism of Leave campaigners Boris Johnson and Michael Gove.

"We must not let emotions be stirred by false fear, nor allow that false fear to impair our judgment on the future of the country."

Meanwhile the governor of the Bank of England, Mark Carney faced calls for his head after he said leaving the EU could push Britain into recession, pointing out that jobs could be lost, the pound would slump and inflation would rise.

The Bank's analysis, backed by its rate-setting committee, said there would be "a materially lower path for growth and a notably higher path for inflation" and warned of another credit crunch.

However Leave campaigners said stepping into a political debate was not within the gift of the governor with Conservative MP, Jacob Rees-Mogg, calling on him to leave.

He told Sky News: "Mark Carney has made a deeply political choice in a referendum which is the concern of the British people and therefore should be fired."

Separately, David Cameron has refused to debate the EU referendum head-to-head with Boris Johnson, choosing instead to agree in a TV debate with Nigel Farage. Eurosceptic Tory MP Andrew Bridgen said Cameron was running scared and told the Daily Mail:"The Prime Minister should be willing to debate against the most credible of the Leave advocates."