Boris Johnson's government is refusing to reveal what they expect the economic impact of his new Brexit will be.

A cross-party group of MPs wrote to Brexit Secretary Stephen Barclay calling for the government to release analysis of how Johnson's deal would affect the UK economy.

However, Chancellor Sajid Javid said: "I see no need for a new impact assessment."

Previous analysis said a free trade deal along the lines of that envisaged in Johnson's deal would reduce annual economic growth by 6.7%.

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BRUSSELS, BELGIUM — Boris Johnson's government is refusing to reveal what the economic cost will be of his new Brexit deal with the European Union, before asking members of Parliament to vote for it.

Previous government analysis suggests that a deal along the lines of that negotiated by Johnson would reduce economic growth by 6.7%, cut wages and cost average households thousands of pounds worse off.

However, speaking to reporters in Washington on Thursday, the United Kingdom's Chancellor Sajid Javid said the government sees "no need [to release] a new impact assessment."

Read more: The EU is preparing to delay Brexit if the UK Parliament rejects Boris Johnson's deal

Labour MP Hilary Benn, who heads the House of Commons Brexit committee, wrote to Brexit Secretary Stephen Barclay this week asking for the government to publish an assessment of how the new deal would impact the economy.

"I trust that the Government will be publishing an impact assessment of this revised deal, and that it will be available to Members of the House in time to inform the debate and vote on Saturday," Benn said.

He added: "Given the significance in particular of the revised political declaration and the Government's previous assessment of the adverse economic impact of a free trade agreement with the EU, I think it is really important that colleagues have the fullest assessment available to them in order to inform their decision."

However, Javid said MPs should do their own research on the deal.

He told reporters that government analysis of the impacts of a free trade agreement with the EU, which is what Johnson's deal points to after Brexit, was "still out there" and "anyone can look it up."

Johnson's opponents vow to block his Brexit deal

Labour's Shadow Brexit Secretary Keir Starmer Getty

Johnson's government faces an uphill battle in trying to get his new deal through the House of Commons and will need the support of around a dozen Labour MPs.

If MPs back the deal, it will allow the UK to leave the EU on the current Brexit deadline of October 31.

However, Labour Shadow Brexit Secretary Sir Keir Starmer said on Thursday that his party "cannot back this deal," primarily because of what it says about the UK's future relationship with the EU in the Political Declaration.

One of the key differences between Johnson's deal with the EU and the agreement negotiated by his predecessor Theresa May is in the Political Declaration, which sets out the UK's preferred future relationship with the EU.

May's Political Declaration called for a tight relationship with the EU after Brexit based on high levels of alignment both in regulations and customs. However, Johnson's indicates looser ties and a simple free trade agreement.

Read more: What is in Boris Johnson's new Brexit deal with the EU and what does it all mean?

Pro-EU campaigners piled more pressure on Javid to publish a new impact assessment.

"The chancellor's refusal to publish information about the impact of Boris Johnson's deal will send alarm bells ringing around the country," Naomi Smith, CEO of Best For Britain, told Business Insider.

"If the deal could stand up to scrutiny, there would no reason to hide the detail.

"Instead, what little we know about the deal shows it's even more of a national humiliation than Theresa May's botched effort.

"That's why this deal must be put to the people for the final say. They've played no part in negotiating this wretched deal, and it would be plain wrong to force it upon the country without their consent."