Dominic Raab has promised to keep a no-deal Brexit on the table while he tries to negotiate a better deal, as he makes his bid for the Tory leadership.
Speaking to the BBC's Andrew Marr on Sunday, he said the negotiations need to be more resolute than before and no-deal should have been left on the table.
The former Brexit secretary revealed his leadership bid in the Sunday papers, along with former Commons leader Andrea Leadsom.
He said while he does not want a no-deal Brexit, Britain is in a weaker position if it is not willing to walk away from negotiations.
"We were not resolute enough and we took no-deal off the table," he said.
"I don't want a WTO Brexit.
"We put ourselves in a much weaker position in terms of getting a deal if you are not willing to walk away from a negotiation - it doesn't focus the mind of the other side."
He added: "I would fight for a fairer deal in Brussels with negotiations to change the backstop arrangements, and if not I would be clear that we would leave on WTO terms in October."
However chancellor Philip Hammond insisted Theresa May's successor would be defying Parliament if they took the UK out of the EU without an agreement.
Mr Hammond said talk of a renegotiation before the end of October was a "fig leaf for a policy of leaving on no-deal terms" and said Parliament had "voted very clearly to oppose a no-deal exit."
He told Marr: "A Prime Minister who ignores Parliament cannot expect to survive very long."
Mr Raab said he wants to lead a Conservative team, but did not rule out working with Nigel Farage's Brexit Party.
When asked if he could do business with Mr Farage, the former Brexit secretary said: "Look, I always listen to all sides of this debate, from Nigel Farage to others.
"But no, I would lead a Conservative team, uniting all the different aspects of the Conservative Party around a cabinet table."
When asked if as leader he would enter an electoral pledge with Mr Farage, he said he had "no plans" for that.
He added: "That's not what I would be aiming for.
"My aim is not to cosy up with other parties, my aim is to keep Conservative promises, present an optimistic, aspirational vision of the future, then go and beat Jeremy Corbyn."
Mr Raab said it is important to deliver Brexit before the next general election.
He said: "We are scheduled for 2022 and I think it's very important we get Brexit delivered before we go back to the polls."
Meanwhile, former work and pensions secretary Esther McVey, who announced her leadership big on Friday, told Sky's Sophy Ridge McVey the UK must start preparing for a no-deal exit straight away.
She added: "October 31 is the key date and we are coming out then, and if that means without a deal then that's what it means.
"We won't be asking for any more extensions."
Former education secretary Justine Greening ruled herself out of the leadership contest on Sunday, calling it "a beauty parade for hard Brexiteers".
Ms Greening told Sophy Ridge the leadership battle is a "narrow discussion in a narrow Conservative Party that's really around what version of hard Brexit to do".
She added: "This should and could be a leadership contest that was about hard choices for the Conservative Party.
"Instead it is really just going to be a beauty parade of hard Brexiteers.
"I am not going to be in it."