Senior European Union officials have dismissed British Prime Minister Theresa May’s Brexit plan as unrealistic. They said the UK has no chance of changing the European Union’s founding principles.

“We read the white paper and we read ‘cake’,” an EU official told the Guardian, a reference to Boris Johnson’s one-liner of being “pro having [cake] and pro-eating it”. Since the British EU referendum, “cake” has entered the Brussels lexicon to describe anything seen as an unrealistic or far-fetched demand.

As reported by The Guardian, May’s white paper is expected to propose the UK remaining indefinitely in a single market for goods after Brexit, to avoid the need for checks at the Irish border. While the UK is offering concessions on financial services, it wants restrictions on free movement of people – a long-standing no-go for the EU.

Jean-Claude Piris, a former head of the EU council’s legal service, said it would be impossible for the EU to split the “four freedoms” underpinning the bloc’s internal market, which are written into the 1957 treaty that founded the European project: free movement of goods, services, capital and people.

“The EU is in difficulties at the moment; the one and only success which glues all these countries together is a little bit the money and the internal market,” Piris said. “If you fudge the internal market by allowing a third state to choose what they want … it is the beginning of the end.”

According to The Guardian, some sources expect the UK to abandon these plans. In an attempt to sweeten the pill they are prepared to offer an extra year of transition to smooth Britain’s EU exit.

The British government believes the EU is guilty of its own cherry-picking, for example, by demanding the status quo on fishing quotas in exchange for zero tariffs on goods.

During last week’s EU summit, the EU’s 27 leaders, minus May, spent no more than 15 minutes discussing Brexit, while only a couple of countries intervened. A terse statement issued by the leaders called on the UK to come up with “realistic and workable proposals”.

In a separate report, the Reuters news agency noted that May on July 3 called for a future customs relationship with the EU in place by the end of 2020 so that a backstop arrangement for the border between the north and south of Ireland would not be required.

“I am very clear that we should be doing everything that we can to ensure that at the end of December 2020 we are able to see our future customs relationship in place such that that backstop is not necessary,” she told Parliament.