MAY DAY: Europe and party rebels round on PM's Brexit plans

Pressure is mounting on British Prime Minister Theresa May from the European Union and from within her own Conservative party over the so-called Chequers plan for Britain's exit from the EU as the UK Parliament prepares to assemble after the summer break.

The EU's chief Brexit negotiator Michel Barnier says he is "strongly opposed" to key parts of May's proposals for a post-withdrawal trade deal.

Former Foreign Secretary and leading 'Brexiteer' Boris Johnson has launched a scathing attack on the plan in what some see as an opening salvo in a campaign to oust May from Downing Street and replace her.

Other anti-EU conservatives such as former "Brexit" secretary David Davis and International Development Secretary Liam Fox have also piled in over the weekend.

Speaking to a German newspaper, Barnier said a suggested "common rule book" for goods would kill the European project.

He told Frankfurter Allgemeine Zeitung: "We have a coherent market for goods, services, capital and people - our own ecosystem that has grown over decades. You cannot play with it by picking pieces.

"There is another reason why I strongly oppose the British proposal. There are services in every product. In your mobile phone, for example, it is 20 to 40 per cent of the total value."

Barnier also told EU car manufacturers they would have to use fewer British parts after Brexit to keep to tariff export rules.

Davis meanwhile went onto BBC television to brand the Chequers blueprint as being "actually almost worse than being in" the EU, a line echoed by Johnson in his Sunday column in the staunchly euro-sceptic Sunday Telegraph.

Davis poured scorn on May's claim that she would not be "pushed into accepting compromises on the Chequers proposals that are not in our national interest" as that risked becoming an "an incredible open sesame to all".

"We will be under the rule of the EU with respect to all of our manufactured goods and agri-foods, that's a really serious concession; what about take back control, it doesn't work?" Davis mused.

"That actually leaves us in a position where they dictate our future rules without us having a say at all, so it's a worse deal."

Fox, also speaking to the BBC, took a swipe at the Treasury over gloomy predictions on the consequences of a no-deal scenario.

"Can you think back in all your time in politics where the Treasury have made predictions that were correct 15 years out, I can't. They didn't predict the financial crisis that happened; no one could," he said.