Britain's Home Secretary Sajid Javid | Tolga Akmen/AFP via Getty Images Ministers will see full Brexit legal advice, says Sajid Javid Whether the legal advice is released more widely will be a matter for the prime minister, he said.

Cabinet ministers will be given the full legal advice provided to the government on the Brexit deal before they sign off on it, said Home Secretary Sajid Javid.

Access to the full advice has emerged as a key demand from Brexiteer ministers who fear that a summary of the legal analysis might omit points that are unhelpful to Prime Minister Theresa May's aim of winning ministerial backing for her deal.

In particular, they want to be sure that the negotiated mechanism for exiting a temporary customs union that will act as a bridge to the U.K.'s future relationship with the EU can be triggered by the British government unilaterally.

Speaking to POLITICO during a trip to Silicon Valley in California, Javid quashed fears that the full legal advice would be withheld from ministers.

“The Cabinet will be seeing … all of the documentation relating to the deal, and that will include the legal advice," he said, "And not just obviously seeing the advice, but the Cabinet has the benefit of actually hearing and asking questions of the attorney general, which I think is very important on something as critical as this."

Whether the legal advice is released more widely is less certain though. "In terms of whether any of the documentation, whether this legal advice, is made more widely available, that has to be rightly a decision for the prime minister,” he added.

In a separate development, the Times reports that May wrote to the Democratic Unionist Party leader Arlene Foster — whose MPs vote with May's government in the House of Commons — to reassure her about the Northern Ireland "backstop" mechanism to avoid a hard border. May said she would not allow the EU's Northern Ireland-only backstop to “come into force” — a change from her previous position that the EU's backstop was "unacceptable."

The DUP has interpreted that wording as meaning that the EU's backstop will nonetheless be included in the Withdrawal Agreement in some form.

“The prime minister’s letter raises alarm bells for those who value the integrity of our precious Union and for those who want a proper Brexit for the whole of the UK. It appears the prime minister is wedded to the idea of a border down the Irish Sea with Northern Ireland in the EU single market regulatory regime,” Foster told the paper.