Employment minister Priti Patel is giving some anxious moments in Downing Street as she is believed to be on the verge of becoming the first member of the cabinet to defy Prime Minister David Cameron and declare herself as a supporter of a Brexit.
She is understood to have demanded an urgent meeting with Cameron after he himself announced he would campaign for Britain to stay in the EU.
Ms Patel has been privately clear that she is reluctant to compromise her anti-EU belief.
According to a report in the Daily Express, she has come under huge pressure from Chancellor George Osborne to stay silent in the referendum as she has been identified as a potential leadership rival who could unite the eurosceptics in the party once Cameron quits.
A Tory source, according to the Daily Express report, said: “It seems she has been told by George (Osborne) that if she campaigns for Brexit he will make sure she does not get a good job when he becomes Prime Minister.”
But he added: “The problem for him is that Priti would be an ideal face for the campaign because the most undecided voters are women and she is a departure from old white men.”
With Home Secretary Theresa May and London Mayor Boris Johnson both indicating that they will back the Remain campaign, eurosceptics are looking for a senior figure to lead the campaign and then potentially become a Tory leadership contender.
Ms Patel is being urged by fellow MPs who believe she would be the perfect figurehead for the group to join the Out campaign.
Meanwhile, the Government said that a British EU exit could mean thousands of refugees landing on Britain’s shores “overnight”.
A “Brexit” could undermine a Franco-British bilateral agreement that allows Britain to carry out border checks on French soil, stopping many refugees and other migrants, a spokesman of Cameron said.
“Should Britain leave the EU there’s no guarantee those controls would remain in place,” Cameron’s spokesman told reporters at a daily briefing on Monday.