The leading Brexiteer Tory MP, who heads the powerful European Research Group, warned the Prime Minister that she risks being caught in a deal which will leave Britain under Brussels rule.
Writing in the Sun on Sunday, he pointed out that the EU has been “dismissive” of her controversial Chequers plan.
He said: “Michel Barnier, who led the negotiations for the EU, has been clear that the EU cannot accept this position.
“The UK must either be in the Single Market with all that goes with it — including free movement — or it may have a free trade deal instead.”
He described Barnier as “the keeper of the Oriflamme for the EU.”
He said: “Historically, this was a sacred banner carried into battle for the kings of France when no prisoners were to be taken.
“The heads of government may be more conciliatory and keener to help a fellow leader, not least as most of them face their own domestic difficulties.
“It is also the usual form for the EU to make a deal.”
He went on: “Chequers rubbed out the Prime Minister’s red lines to leave the UK ‘half in, half out’ subject to EU regulations in crucial areas of the economy, and to the European Court of Justice.
“The vassal has been put in chains.
“This desperation means it will be important to watch carefully what comes out of Salzburg.”
He also warned that because of the hostile comments from the EU that any deal will be seen as “a triumph of British diplomacy” but he warned Brexiteers “need to stay awake”.
He said: “If we pay £40billon we must get something clear in return, not just wishy-washy promises.
“Taxpayers would be outraged if it were otherwise.
And he added: “Any agreement on immigration must be examined with great care.
“We will doubtless be told that free movement has ended but, as Shakespeare wrote, “what’s in a name? that which we call a rose by any other name would smell as sweet”.
“There ought to be no preferential terms for new arrivals from the EU above those offered to other nations and no access to state benefits.”