Cabinet minister Andrea Leadsom warned European Union Brexit negotiators not to try to tear up Theresa May’s plans because doing so would force the U.K. into a “no-deal” situation where it crashes out of the bloc.

The EU must accept that the deal agreed by most of May’s Cabinet at her Chequers country house this month is the “final offer,” and take the U.K. “seriously” as it ramps up its no-deal preparations, Leadsom said. She conceded that adopting World Trade Organization rules for trade with the bloc “would not be the optimal solution,” but said the U.K. would still thrive economically.

“What this deal does is it says to them, ‘right, now we can have a free trading area where there won’t be the need for border checks and controls,”’ Leadsom, a Brexit supporter, told Parliament’s The House magazine.

In the same magazine, Foreign Secretary Jeremy Hunt said May’s Chequers deal is “absolutely alive” and will be “key to unlocking” talks with Brussels. It’s also the “only way” to secure frictionless trade with the bloc—something “every Conservative should support,” he said.

Meanwhile, the European Commission published a document calling on governments and businesses to boost contingency plans for Brexit talks collapsing without a deal. Preparation must “be stepped up immediately at all levels and taking into account all possible outcomes,” it said.