Senior ministers are arguing that the controversial Irish backstop issue that stands in the way of a Brexit deal can be solved if the UK commits to a form of permanent customs union with the EU, BuzzFeed News has learned.

Sources across Whitehall are increasingly convinced they will be able to secure a political win by adding either an end date or an exit mechanism to the backstop — the insurance policy to prevent a hard border — that the House of Commons says has to change for a Brexit deal to pass.

But while ministers are publicly calling on the EU to recognise Tuesday night’s vote that MPs want the backstop to be replaced by “alternative arrangements”, privately they accept that any concession from Europe will come at a price.

One proposal being suggested by ministers and MPs is for the UK to make a commitment in the political declaration outlining the future UK–EU relationship to join a version of a permanent customs union. This commitment could “neutralise” the backstop and see the EU give way on an end date or exit clause, the MPs believe.

Staying in a customs union would remove the need for customs-related checks between the UK and the EU, including at the Irish border — a crucial element of the backstop.

“It could be possible to change the backstop in exchange for some sort of permanent customs union or arrangement in the political declaration,” said a government source, stressing this was just one option being looked at. “It would not be a fig leaf, it would be a fig tree.”

Theresa May has so far insisted that the UK will leave the customs union, as well as the single market, in order to strike ambitious trade deals around the world and end the free movement of people. In her Lancaster House speech of January 2017, May said she had an “open mind” about a customs agreement with the EU.

Brussels has been firm in making clear that the prime minister is the one who needs to compromise on her red lines if she wants to change the dynamics of the overall deal.