British Foreign Secretary Boris Johnson on Tuesday dismissed as "crazy" a government proposal for customs arrangements with the EU after Brexit, forcing cabinet divisions into the open once again.
Johnson, an outspoken supporter of Britain's withdrawal from the European Union, said the plan backed by Prime Minister Theresa May would not fulfil many of the promises of Brexit.
"If you have the new customs partnership, you have a crazy system whereby you end up collecting the tariffs on behalf of the EU at the UK frontier," he told the Daily Mail.
He added: "If the EU decides to impose punitive tariffs on something the UK wants to bring in cheaply there's nothing you can do."
Citing the pledges of the Brexit campaign, Johnson said: "That'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, because tariffs would get paid centrally back to Brussels."
London has put forward two options to ease cross-border trade with the EU, and -- with Brexit looming in March next year -- the bloc is waiting for a final decision.
May's preferred option, the customs partnership, was reportedly rejected at a cabinet meeting last week.
Downing Street admits the plan, which would involve Britain collecting EU tariffs on goods heading into the bloc but charging its own on UK-destined products, is untested.
A second option, the so-called "maximum facilitation" option, would involve using technology to minimise customs checks but would likely not reduce them as much as the first proposal.
Business Secretary Greg Clark made the case on Sunday for the prime minister's preferred option, highlighting the importance of reducing "frictions" to firms dependent on complex, cross-border supply chains.
He cited Toyota, which employs 3,500 people in two British manufacturing plants, saying the customs partnership model would allow them to import parts from elsewhere "without any checks at the border".
"You can compare models but actually you need to have in mind the future jobs but also the very important jobs for people today," he told BBC television.
Johnson dismissed his warning as "Project Fear".
A final decision is not expected to be taken for at least another week, ahead of a crucial EU summit in June.