Liam Fox has said the decision as to whether to end the Brexit backstop has to be for the UK alone – in a challenge to Theresa May.

The international trade secretary said on Thursday the government had “an instruction from our voters to leave the EU”.

“That decision can’t be subcontracted to somebody else that needs to be an issue for a sovereign British government to be able to determine,” he told Sky News.

Brexit talks had been deadlocked over the so-called backstop – the fallback position that would be activated if a future EU-UK trade deal does not produce a solution that would prevent a hard border between Ireland and Northern Ireland.

Amid speculation a deal is closed to being agreed, May’s proposed backstop would see the entire UK effectively agree to remain in the customs union.

Brussels has said the UK will not be able to dissolve the backstop without agreement from the EU.

But Brexiteers want the British government to have the power to unilaterally end it.

Some cabinet ministers want to see the full legal advice given to May setting out how any customs arrangement could be ended to avoid it becoming a permanent settlement.

Labour has also demanded the legal advice, drawn up by Attorney General Geoffrey Cox, should be made public.