LONDON

British Prime Minister Theresa May still has confidence in Boris Johnson, her spokesman said, after the UK foreign secretary described his boss’s post-Brexit trade policy with the European Union as “crazy.”

The prime minister’s proposal for a customs partnership with the EU — a complicated plan that would keep the UK closer to the bloc than Brexit backers would like — was rejected by most of her Cabinet last week and Eurosceptics declared it dead. May is optimistic her ministers will agree on a way forward, her spokesman, James Slack, told reporters in London.

“There were good discussions last week and we are working to refine those models,” Slack said. “December 2020, we will be leaving the customs union.”

Under a customs partnership, the UK would collect tariffs on behalf of the EU and then refund exempt businesses.

Johnson said in an interview with the Daily Mail that May’s plan was “totally untried” and a “crazy system” for organising customs and borders after the divorce. It’s “not taking back control of your trade policy, it’s not taking back control of your laws, it’s not taking back control of your borders and it’s actually not taking back control of your money either,” he said.

But May needs her plan to survive as her team sees it as the only way to deliver the Brexit she has promised. The alternative would be a messy no-deal split or staying in the EU’s customs union — would be seen as a breach of her word that would probably prompt a leadership challenge.