British Prime Minister Theresa May has called on Conservative Party MPs to support her when the EU Withdrawal Bill is discussed in the House of Commons this week.

She said they should reject 14 of the 15 amendments suggested by Britain's second chamber, the House of Lords, when they are debated on Tuesday and Wednesday.

"We must think about the message Parliament will send to the European Union this week," she said, explaining that Tory rebels would tie her hands during Brexit negotiations if they opposed her.

"I am trying to negotiate the best deal for Britain. If the Lords amendments are allowed to stand, that negotiating position will be undermined."

May has a working majority of only 13 MPs, thanks to the support of a minor party, and could be defeated if seven pro-EU Tories side with the opposition.

The Financial Times newspaper said Tory party whips were concerned pro-EU Conservative rebels could scupper May's Brexit plans.

But it said that Remain and Brexit-supporting MPs were set to get behind the government and defeat an amendment on Wednesday that would force May to give MPs a decisive say in the autumn on any final deal she strikes with the EU. May fears that amendment would give the EU's chief negotiator, Michel Barnier, the opportunity to sideline her and negotiate directly with Parliament.

The BBC reported that David Davis, Britain's Brexit secretary, had written to Tory MPs saying it was "simply not right" that Parliament could try to overturn the referendum result in such a roundabout way.

He told BBC Radio 4: "Whatever we do, we're not going to reverse that (decision to leave the EU)."

Meanwhile, the Telegraph reported that Justice Minister Phillip Lee had resigned from the government so he can speak out against Brexit.

In an opinion piece on Tuesday, The Guardian's Keir Starmer said, with Tory revolts, David Davis reportedly on the verge of resigning, and Boris Johnson telling supporters Donald Trump would make a better negotiator, "it is now clearer than ever that May will fail to deliver the Brexit deal that Britain needs".

And CNN said that, after months of talk, this week marks a moment of truth for May and her government.

Tory rebels will get another chance to amend Brexit legislation when the customs and trade bills are discussed by Parliament next month.

Britain is set to leave the EU on March 29.