Boris Johnson warns Theresa May to keep her word amid customs union row

Boris Johnson has issued a veiled warning to Theresa May to “be true to her promise” to leave the EU’s customs union, rather than triggering a “backstop” that would tie Britain to the arrangements beyond 2020.

The foreign secretary told his Eurosceptic colleagues to give Ms May “time and space” to negotiate a deal with Brussels that would give Britain a clean break after Brexit and left the prime minister in no doubt of his opposition to any extension of EU rules.

Cabinet ministers have been at loggerheads for weeks over post-Brexit customs arrangements, with Mr Johnson previously describing Ms May’s favoured customs partnership plan as “crazy”.

The government is currently working on a backstop scheme that would extend the period of time during which the UK would remain within the EU’s customs union, as part of efforts to resolve the Irish border issue.

Speaking to reporters on a trip to Latin America, Mr Johnson said: “Brexiteers fearing betrayal over the customs backstop must understand that the prime minister has been very clear that neither option is an outcome we desire – we want a deal with the EU and she will deliver it.

“I’m convinced that the prime minister will be true to her promises of a Brexit deal – that sees Britain come out of the customs union and single market, have borders as frictionless as possible, reject European Court of Justice interference, control immigration and free to conduct unhindered free trade deals across the world.

“We must now give the prime minister time and space to negotiate this Brexit vision.”

Mr Johnson was reportedly one of the two ministers who unsuccessfully argued against the backstop option in last week’s Brexit war cabinet, amid fears from Brexiteers that it would lead to an indefinite extension of EU rules.

The plan was devised as an alternative proposal to the EU’s suggestion that Northern Ireland should remain in the customs union if the border wrangle cannot be solved.

However, Ms May roundly rejected the plan as it would draw a customs border down the Irish Sea.

The intervention came as Mr Johnson embarked on a five-day trip to Peru, Argentina and Chile on a mission to drum up post-Brexit trade deals.

He is the first British foreign secretary to visit Argentina in more than 20 years as the UK seeks to repair its relationship with Buenos Aires.

In a sign of the efforts to reset the relationship, Mr Johnson paid his respects at the memorial to Argentine troops killed in the 1982 Falklands conflict, leaving a wreath in memory of all those who died on both sides.