British Prime Minister Boris Johnson is facing the moment of truth for his Brexit strategy as he prepares to present his blueprint for a deal to the European Union in days.

The reception his plan receives in Brussels and among pro-Brexit members of his ruling Conservative Party will determine whether there is any hope of securing an orderly exit for the U.K. by the end of this month.

If Johnson’s strategy fails, he will face a choice between seeking another delay to the Oct. 31 deadline — something he says he will never do — or trying to force the country out of the EU with no deal, which his opponents in Parliament have moved to stop.

While there are signs that purist euroskeptics in Johnson’s Tory party are willing to compromise and back a deal to secure Brexit, he will struggle to convince the EU to accept his proposals. Irish Foreign Minister Simon Coveney said on Tuesday that what has been put forward so far is a non-starter.

The U.K. is due to leave the EU on Oct. 31 and Johnson says he is determined to deliver Brexit on time — even if that means doing so with no deal to cushion the impact on trade.

Any agreement must pass through Parliament in London but Johnson’s predecessor, Theresa May, tried and failed three times to win backing for the contract she negotiated with the bloc. The key sticking point remains how to ensure there are no checks on goods crossing the land border between the U.K. and Ireland.

For Johnson, a key demand is to ensure Britain is not trapped indefinitely in the so-called “backstop” arrangement, which would tie the U.K. into the EU’s customs rules, defeating the point of Brexit.

But there is a risk that what Johnson is asking for is unacceptable in Brussels. Irish broadcaster RTE reported late Monday that the U.K. has proposed customs checks five to 10 miles away from the Irish border. That may be rejected by the EU side.

A U.K. government spokesman said Johnson was not proposing any customs controls at the Irish border. One British official added that Johnson’s team expected most checks on goods to take place away from the frontier, either at dedicated premises or at the destination. It would be up to the customs authorities to decide where to conduct checks.

Johnson is vowing to use the final month before Brexit day to step up efforts to get a deal that will be acceptable in both Brussels and London. He’s likely to present his plans in Brussels later this week. The EU wants to know that any deal it signs will win the backing of the U.K. Parliament.

The most difficult group Johnson needs to win over is arguably the 28 so-called “Spartans” — pro-Brexit Conservatives who voted against May’s deal three times and ultimately forced her out of office.

When May tried to persuade hardline Tory euro-skeptics to back her agreement, they refused because they believed a purer form of Brexit option was available. This time, they’re not sure that’s true.

“It’s no longer a question of ‘we could do better,'” Andrew Rosindell, one of the Spartans, said in an interview. “We’ve reached the end of the road.”

The Tory hardliners on their own aren’t enough to pass a deal. Johnson would still probably need the support of Northern Ireland’s Democratic Unionist Party, and some Labour MPs. Here, too, there were positive signs on Monday.

DUP leader Arlene Foster said she’s willing to look at the idea of a time-limit on the contentious Irish border “backstop” — a policy designed to ensure there are no checks on goods crossing the U.K.-Ireland frontier.

If a deal looked close to passing, some of the more than 20 Labour MPs who have said they’d be willing to vote for one might do so, to get Brexit finished.

Greek Warriors

In September, members of Parliament took the unprecedented step of forcing through a new law — against the government’s wishes — to stop Johnson enacting his threat to exit the EU with no deal. That radical move has changed the calculation for the so-called Spartans.

The group takes its name from the Greek warriors who held off the Persians at the Battle of Thermopylae in 480 BC.

Some of these pro-Brexit Tories fear that Johnson could be forced to delay Brexit again, and would then find himself fighting a general election having broken a promise to get Britain out of the EU. The Tories would then be vulnerable to losing votes to the Brexit Party of Nigel Farage, and ultimately at risk of being ousted by Jeremy Corbyn’s Labour.

“An extension this time would mean an election,” Rosindell said in Manchester, England, where the Tories are holding their annual conference. “If we hadn’t got out by Oct. 31, the chances of a Corbyn government are very high.”

He’s not the only hardliner showing a willingness to compromise. Mark Francois, deputy chairman of the pro-Brexit European Research Group, told a meeting at the Conservative conference that some form of “backstop” to deal with the contentious issue of how goods moved between Northern Ireland, in the U.K., and Ireland, still in the EU, wasn’t necessarily a problem.

“If there is some form of deal, be it over the backstop or anything else, then I and my colleagues will look at it and read it very carefully,” he said. “At the end of the day, we’re talking about international treaty law. My acid test will be does it genuinely mean we leave the EU.”

One of the government officials involved in drafting the British proposal said it would be acceptable to the Brexit hardliners.

According to Rosindell, they’re now a receptive audience. “Boris will be in a much better position than Theresa was six months ago,” he said. “It’s much more likely that we would vote for it, if it’s an improved deal.”

–With assistance from Ian Wishart and Kitty Donaldson.