Theresa May is struggling to stave off a landslide defeat of her Brexit deal in parliament next week.

In a last ditch bid to save her deal she offers MPs a vote on the controversial Brexit 'backstop'.

The backstop would keep the UK locked to EU trade and customs rules if it fails to secure an alternative deal with the EU at the end of the tw0-year transition.

May's offer would allow MPs to direct her to extend the transition period instead.

Conservative Brexiteers dismiss May's offer as "ludicrous."

LONDON — Theresa May will offer MPs a vote on whether to trigger the so-called Brexit backstop, as she struggles to avoid a humiliating parliamentary defeat next Tuesday.

The prime minister said that Parliament could be given a choice whether to trigger a backstop or extend the Brexit transition period, if no deal on the UK's future relationship with the EU is found by the end of 2020.

Under the terms of the deal May has agreed in principle with the EU, the UK will be forced to remain in a customs union with EU if a deal is not reached by that point, while Northern Ireland will stay in parts of the single market.

The backstop is unpopular both among Conservative Brexiteers who believe it could keep the Britain indefinitely tied to the EU and Democratic Unionist Party MPs propping up May's government who say it is a threat to Nothern Ireland's status in the UK.

However, the prime minister said on Thursday that parliament could choose to avoid this scenario by instructing the government to extend the transition period instead.

"The backstop is not automatic. I'm looking at the role of Parliament in that choice," she told the Today programme.

She added that there were "pros and cons" to either option, saying that the backstop would not involve paying any more funds to the EU, whereas extending the transition would require an additional fee, plus accepting the continuation of freedom of movement with the EU.

The offer was immediately dismissed by Conservative Brexiteers.

One source in the anti-EU European Research Group of Conservative backbenchers, told Business Insider that May's offer of a vote was "ludicrous."

"The problem that needs fixing doesn’t need fixing here, it needs fixing in Brussels. Indeed the whole problem is that the problem can only be fixed in Brussels," the source said.

They added: "Saying 'Let me solve the problems in an international treaty with Westminster procedural flim flam' is not very convincing. Least of all with a bunch of Westminster proceduralists."

DUP threatens to bring down the government

May made the offer as Conservative whips fought to stave off what could be a defeat of historic proportions next week.

The prime minister has repeatedly fielded questions from concerned Conservative backbenchers both in private and in the Commons. However, all the signs are that opposition to her deal with the EU is refusing to budge.

Last night Conservative rebels met to discuss what to do should May's deal be defeated next week. Conservative MP Jacob Rees-Mogg, who chairs the ERG, told the group that the DUP had told him they would withdraw their support from May's government if the deal went through, but would retain it if it is defeated.

The meeting was also joined by chief Conservative whip Julian Smith. One ERG source told Business Insider that Smith had achieved "no traction" with the group.

"He was politely received with no shouting in either direction, but there was equally no traction," the source said.