MPs will not know “the full details” of Britain’s future trade deal with the EU when they vote on Brexit later this year, the Chancellor has admitted.

Philip Hammond was accused of having “let the cat out of the bag” with the comments, which contradict David Davis’ insistence that the negotiations will conclude before departure day.

“He wants MPs to vote with their eyes closed on the final deal – and to ignore the serious damage Brexit will do,” said Caroline Lucas, the co-leader of the Green Party and supporter of the pro-EU Best for Britain group.

On Wednesday, the Brexit Secretary tried to reassure MPs that “all of the substance” of the UK’s future relationship with the EU will be agreed before Brexit, in March next year.

But, speaking to financial newswire Bloomberg, Mr Hammond conceded that the details of any agreement would not be clear before Parliament votes on withdrawal terms, probably this autumn.

He said: “Probably not the full details, but we would expect the high level shape of the future relationship to be emerging by that time.”

Ms Lucas added: “MPs need to be able to vote with the full facts in front of them, anything else would be utterly unacceptable.”

The comments are also likely to further inflame growing tensions with hard Brexit supporting Conservative MPs, who are threatening a revolt over the planned transition deal.

It would also mean Parliament being asked to authorise the £39bn “divorce bill” in the withdrawal agreement, before details of the trade agreement are hammered out.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

In the interview, Mr Hammond also made clear that securing access to the EU markets for financial services firms would be a red line for the UK.

But he said that might not be formal “passporting” arrangements – allowing companies to operate across the EU unhindered no matter where they are based – which Brussels has already ruled out.

Nevertheless, Mr Hammond said he believed the UK had a negotiating advantage on the issue of financial services being included in the deal.

“We have to negotiate that with the European Union but the UK’s financial services sector is larger than the rest of the European Union’s put together, so we have some negotiating weight in this discussion,” he said.