EU's chief Brexit negotiator Michel Barnier warned Wednesday that Britain's appetite for an ambitious trade deal with Europe after Brexit could go badly unsatisfied given Prime Minister Boris Johnson's demands.

Speaking to MEPs in the European Parliament, Barnier regretted that Johnson's new government had expressed its intention to "reverse the commitments" on trade made by his predecessor Theresa May.

These pledges were part of a non-binding "political declaration" on the future relationship between the EU and UK. It stands beside a highly contentious, binding withdrawal deal which has failed to win approval in British parliament.

In addition to rejecting the divorce terms, Johnson's negotiators have asked that Britain be allowed to widely diverge from EU rules after Brexit, all while securing a highly ambitious trade deal with Europe.

European Parliament's Brexit coordinator, MEP and former Belgian prime minister Guy Verhofstadt, dismissed that stance.

"We are not stupid and we will not kill our own companies. We will defend our own economy and we’ll never accept Singapore by the North Sea," he said to cheers and boos from MEPs.

No deal 'not a destination'

A senior EU official explained to AFP that Johnson's suspected bid to turn the UK into a "Singapore" of Europe meant making it a country where multi-nationals can flout EU rules but keep undisturbed access to Europe's market of 500 million consumers.

The EU has flatly rejected Britain's requests, the official said.

Barnier publicly poured cold water on that British position, insisting that a comprehensive trade accord could only come by closely abiding by EU rules.

"The level of ambition of a future free trade agreement that we will have to negotiate... will clearly depend on the guarantees that we have agreed in the social, environmental, competition or state aid fields," Barnier said in Strasbourg.

"This economic relationship must obviously be accompanied by guarantees of a level playing field," he added, referring to a commitment by trading partners to abide by the same norms.

The brinkmanship comes as London and Brussels are struggling to agree changes to the withdrawal deal, with Britain on course to leave the EU on October 31.

"If the United Kingdom comes out without an agreement, I want to remind you that all these issues do not disappear," Barnier said.

"No deal is not a destination, it is a temporary step -- building a partnership must then be discussed again," he added.