The campaign for Britain to leave the European Union has taken a two percentage point lead, according to an ICM poll, indicating a dispute in the Conservative Party may have dented confidence in Prime Minister David Cameron's push for the country to stay in.

Support for Britain to leave the European Union rose to 43 percent, up 2 percentage points from a similar poll a week ago, the ICM poll indicated.

Three months before the June 23 referendum, the poll of 2,000 people carried out March 18-20 showed the "In" campaign on 41 percent, down from 43 percent a week ago.

Cameron faces one of the deepest crises of his decade-long leadership of the Conservative Party after senior cabinet minister Iain Duncan Smith, who opposes EU membership, resigned over spending on welfare.

Divisions over EU membership - an issue that helped sink the Conservative premierships of Margaret Thatcher and John Major - have amplified such disputes within the party.

"One might wonder how, if at all, this will affect public confidence in the PM and his campaign to keep us in Europe," ICM said in a statement.

"Well, public opinion does not appear to be moving in his favour. Last week's two-point lead for Remain/In is reversed to a two-point lead for Leave," ICM said.

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