"Don't worry, be happy", joked EU chief executive Jean-Claude Juncker after telling reporters after a summit in Austria that the Europeans had full plans in place in the event there was no deal before Britain leaves next March.
Another posted: "Your hubris and smugness know no end, do they, Tusky?"
Tariffs of 10 percent under World Trade Organization rules would add an average of 3,000 euros to the cost of British-built cars sold in the EU if fully passed on to buyers, and 1,700 euros to the cost of a European auto imported into Britain, the SMMT said.
As EU leaders lined up to demand more compromises from the UK, May tried to pile the pressure back on Brussels.
But the European Union has reservations about the plan, and the two sides remain divided over how to ensure there is no hard border between the U.K.'s Northern Ireland and European Union member Ireland.More news: Kanye West Warns Drake, Nick Cannon to Stop Talking About Kim K.
However both sides still want a broad-brush description of the relationship, to avoid a so-called "blind Brexit" without a good idea of how trade and borders will work after the transition.
But the path to the seems far from clear, with the European Council President, Donald Tusk, warning the UK's proposals will need to be reworked.
The Prime Minister said the Chequers blueprint is the only proposal on the table as the deadline approaches, with the next leaders' meeting in October set to be a "moment of truth".
Malta's prime minister on Thursday (20 September) signalled unexpected support from European Union leaders for a second referendum on Brexit in Britain, boosting a growing campaign for a new poll despite the British government's trenchant opposition. "In October, we expect maximum progress and results in the Brexit talks".
Over dinner in Salzburg on Wednesday evening, May told the other leaders that Britain would not delay Brexit or hold a second referendum.
"Everybody shared the view that while there are positive elements in the Chequers proposal for economic cooperation, the suggested framework will not work - not least because it risks undermining the single market", Tusk told reporters.More news: Spiders are 'having a party' in this terrifying 1,000-foot web
"I'm very unhappy that (the) United Kingdom is leaving so it would be better maybe to make another referendum and maybe the people in the meantime they could change their view", he told the BBC.
"It has been clear for weeks that Theresa May's Chequers' proposals can not deliver the comprehensive plan we need to protect jobs, the economy and avoid a hard border in Northern Ireland", he said.
"There are some issues where we are not ready to compromise", Tusk said.
"We can not afford a "no deal" Brexit".
However hard Brexiter David Davis, the former Brexit secretary who resigned in protest over the Chequers plan, predicted on Thursday morning the European Union would push Britain into a deal that would "likely look an very bad lot like [EU] membership".
Speaking after a two-day summit in Salzburg, Mr Macron took aim at leading Leavers, saying: "Those who explain that we can easily live without Europe, that everything is going to be alright, and that it's going to bring a lot of money home are liars".More news: Demi Lovato's mum says she's 'doing really well'
"It's the duty of me as prime minister, of the Government, of politicians across the House of Commons to deliver on that vote".