David Cameron has not closed the door on Government ministers campaigning on opposing sides in the referendum on Britain's EU membership, Downing Street has insisted.

The Prime Minister's official spokeswoman said that no decision has yet been taken on whether the principle of collective responsibility will be enforced on ministers during the referendum campaign.

Mr Cameron sparked consternation among some Tories with comments at the G7 summit in Germany in which he appeared to suggest that ministers could be sacked if they wanted to campaign for British exit after what he deems to be a successful renegotiation of the terms of the UK's membership.

The Prime Minister said the Government will not be 'neutral' on the issue of whether the UK leaves the union, adding: 'If you want to be part of the Government you have to take the view that we are engaged in an exercise of renegotiation to have a referendum and that will lead to a successful outcome ... Everyone in government has signed up to the programme set out in the Conservative manifesto.'

But Number 10 insisted that the PM had been referring only to the need for ministers to observe collective responsibility during the process of renegotiation, which he kicked off following last month's general election victory.

'The Prime Minister was clearly talking yesterday about the position of collective responsibility during the renegotiation - a position the PM has set out previously, including in the House during the Queen's Speech debate,' said the official spokeswoman.

The spokeswoman said that it would be an 'over-interpretation' of the PM's comments to suggest that he was at this stage threatening that ministers could face the sack if they want to vote for Brexit.

Asked whether the principle of collective responsibility would be enforced during the referendum campaign, she said: 'He has not set that out and we are not getting into any hypotheticals on the approach to the referendum.'