David Cameron has left the door open for Government ministers to campaign for Britain to leave the EU in the forthcoming referendum, insisting he will not announce until nearer the time whether they will be bound by the doctrine of collective responsibility.

The Prime Minister said he had been "misinterpreted" in widespread reports which suggested he would sack ministers who refuse to fall in line with his view in the poll, which he has promised by the end of 2017.

But he made clear that the Government will not take a neutral stance in the referendum campaign, insisting: "I don't believe the Government will be a bystander in this. The Government will have a clear view."

Mr Cameron has kicked off the renegotiation of Britain's membership which he hopes will allow him to recommend a Yes vote in the referendum.

At least 50 Tory MPs, including former Cabinet ministers Owen Paterson and John Redwood, have signed up to the newly-formed Conservatives for Britain (CfB) group, which says it is ready to campaign for British exit even if the PM believes that staying in would be in the national interest.

Belfast Telegraph