Jeremy Hunt says Boris Johnson's public outbursts are undermining Brexit negotiations.

The Health Secretary says the foreign secretary should get behind the prime minister.

Hunt's comments are the most public sign yet of a looming war inside May's Cabinet over Brexit.

The UK government has yet to decide what sort of trading relationship it wants with the EU.

There are just 10 months left until Brexit.

LONDON — The bitter divisions in Theresa May's government over Brexit spilt into public on Monday as the Foreign Secretary Boris Johnson was accused by one of his senior cabinet colleagues of undermining Brexit negotiations.

Johnson hit the headlines last week after publicly labelling May's preferred plan for post-Brexit customs arrangements "crazy."

Asked about the comments on Monday, the Health Secretary Jeremy Hunt accused Johnson of undermining Brexit negotiations.

"I do think it's important we have these debates in private, not just because of collective responsibility which is what democracy depends on, but also because this is a negotiation and so on the EU side if they see divisions in the open then they will exploit that," he told the Today programme.

He added: "We have to recognise we're not the only ones who read the papers in Britain. They're read all over the world."

Hunt, who has previously been tipped as a potential successor to May, urged Johnson to keep his thoughts within government.

"We are going to have these lively debates [but] we should have them in private because that will strengthen Theresa May's negotiating hand," he said.

Asked if Johnson should "belt up," Hunt replied that the whole Cabinet should now "work as a team".

Hunt's criticism of a senior colleague is the most public sign yet of growing cabinet divisions over Brexit. Last week May set up two cabinet working groups to help develop the two main post-Brexit customs options being considered by the government. The groups, which are each filled with ministers opposed to the plan they are tasked with developing, are set to update the prime minister on their progress later this week.

The Environment Secretary Michel Gove yesterday joined Johnson in publicly criticising May's preferred option of establishing a so-called "customs partnership" with the EU.

Both options have already been dismissed by EU officials as "magical thinking."