Britain's Prime Minister Theresa May is seen outside Downing Street in London, Britain, February 12, 2019.
He also accused the Prime Minister of "recklessly running down the clock" so that MPs would have to vote for her Brexit deal.
Prime Minister Theresa May has called on MPs to "hold their nerve" and come together behind an European Union withdrawal deal which will deliver Brexit on time on March 29.
But Mrs May fuelled anger she is playing for time to reach March 29 by refusing to give a firm date by which a final vote on her deal will be held.
His remarks to reporters came after talks with EU Brexit negotiator Michel Barnier.
She said she had still not yet decided which of three potential options she will pursue - a unilateral exit mechanism; a time-limit; or the hi-tech solutions envisaged in the so-called "Malthouse compromise".
Justice Minister Rory Stewart told the BBC on Monday that differences between the two aren't as great as some suggest, but the government can't accept a customs union that would prevent Britain from negotiating trade deals with other countries.
She told Sky News: "I absolutely do not think that should be our policy".
However he agreed to further talks to find a way forward, and the pair will meet again before the end of February to "take stock", May said.
MPs and peers, including former ministers Phillip Lee, Sam Gyimah, Guto Bebb and Lord Willetts said her current Brexit deal "risks further dividing our nation and costing jobs" and is "highly unlikely" to benefit families and communities.
And there were signs of unease in Tory ranks at the idea of Mrs May exploring means of bringing the Labour leader on board in her search for a Brexit deal. Now is not the time to stand idly by, now is the time to stand up and do the right thing: to rule out No Deal and back Labour's alternative plan.
Luckily for May, the Tory's confidence-and-supply partners the DUP had her back, helping her avoid a chain of events that could have led to a general election (only 306 MPs said they had no confidence in the government, versus 325 in favour of the party).
May has indicated, to the fury of Brexiters, that she is prepared to negotiate with Corbyn, raising their suspicions she might opt to ask the EU for Britain to remain permanently in the customs union, a deal she could get the Commons to endorse by seeking cross-party support.
Rather than insisting it is removed altogether, however, former foreign secretary and two-time London mayor Johnson said Monday he could support the Prime Minister if she was able to get the European Union to agree to a time limit or other exit mechanism for the backstop.
But she insisted her deal already met numerous conditions he had set, without tying the United Kingdom in to a customs union arrangement which would prevent Britain from striking its own trade deals.
Labour's demands include a permanent customs union, close alignment with the single market and "dynamic" compliance with EU regulations in the areas of the environment, education and industrial regulation.
May said: "Opposing no deal is not enough to stop it".
The prime minister is essentially asking for more time to get something to show for her promise of changes to the controversial backstop.
She did however highlight the "fundamental negotiating challenge" this would entail, namely that Corbyn's proposal would require the United Kingdom to remain in the single market and accept free movement, something which contradicts Labour's manifesto.
Treasury chief secretary Liz Truss refused to rule out resigning if Mrs May backed a customs union.