U.K. Prime Minister Boris Johnson's latest proposal to take his country out of the European Union would divide Ireland and therefore "is unlikely to work," a strategist said on Thursday.

The U.K. currently has until Oct. 31 to leave the EU — with or without a deal. That deadline has been pushed back multiple times after former Prime Minister Theresa May's withdrawal agreement was thrice rejected by the British parliament.

One major sticking point in the Brexit process is the so-called Irish backstop. May's deal had sought to ensure there's no hard border between the U.K.'s Northern Island and EU member Republic of Ireland. But avoiding customs checks there would bind Britain to the bloc's trade rules — a point that Brexit supporters had opposed.

Johnson's proposal, meanwhile, includes an "all-island regulatory zone on the island of Ireland" that would involve customs checks that could be carried out away from the border at "other points on the supply chain."

"I'm not saying it's a complete sham because it moved forward on one particular point ... Boris did widen the scope, but the actual ins and outs of it are unlikely to work," David Roche, president and global strategist at Independent Strategy, told CNBC's "Squawk Box Asia."

"He wouldn't put customs posts at the border but he would put customs clearance areas close to the border — what's the difference?" asked Roche. "If you start putting customs posts on the border in Ireland, you'd have divided Ireland. And that's a great big no-no for the EU and therefore, not going to happen."

Johnson had on Wednesday presented his proposals to the EU. The bloc's chief Brexit negotiator Michel Barnier said there's still a lot work to be done to achieve the three objectives for the Irish backstop: no border, an all-Ireland economy and protecting the European single market.

Barnier added that a no-deal Brexit "will never be the choice of the EU." But Johnson said if the U.K. fails to get a deal, Britain would then leave without one.

— The Associated Press contributed to this report.