COVENTRY: British opposition leader Jeremy Corbyn yesterday called for a new customs union with the European Union after Brexit in a policy shift that could force Prime Minister Theresa May to change course.

Just days before a keynote speech by May on her desired future trading relationship with the European Union, the Labour leader drew a clear line between his policy and that of the government.

"Labour would seek to negotiate a new comprehensive UK-EU customs union to ensure that there are no tariffs with Europe and to help avoid any need whatsoever for a hard border in Northern Ireland," Corbyn told an audience in Coventry, central England.

Britain is currently part of the EU's customs union, which has a common external tariff on imports, allowing goods to move freely inside the area.

But it would leave after Brexit in March 2019.

Citing the example of integrated supply chains in the car industry, Corbyn said it "makes no sense" for Britain to turn its back on "tariff-free trading rules that have served as well".

The Confederation of British Industry, Britain's big business lobby, has also called for a customs union with the EU.

Normally such unions preclude members from doing their own trade deals with other countries -- the reason the option has been ruled out by May.

Corbyn offered a caveat, saying: "The option of a new UK customs union with the EU would need to ensure the UK has a say in future trade deals."

Foreign minister Boris Johnson, a leading Brexit supporter, accused Corbyn of cynicism.

"Corbyn's Brexit plan would leave UK a colony of the EU -- unable to take back control of our borders or our trade policy," he said on Twitter.

"White flag from Labour before talks even begin."

The prime minister's spokesman was unequivocal: "The government will not be joining a customs union. We want to have the freedom to sign our own trade deals and to reach out into the world."