Jeremy Hunt, one of the leading candidates vying to succeed Prime Minister Theresa May, said he would leave the European Union without a deal, but with a heavy heart.
He added that he hoped the bloc would engage with a new British leader.
Hunt said: “Our failure to deliver Brexit has put our country and our party in grave peril.
“The leadership I offer is based on one simple truth: without Brexit, there will be no Conservative government and maybe no Conservative Party.
“If we want a deal, we are going to have to engage seriously with Brussels.
“From my conversations with European leaders, it is clear to me there is a deal to be done, they want us to come up with proposals.”
Hunt, who is foreign secretary, said with a “more aggressive Russia” and a “more autocratic China”, he would boost defence spending if he became prime minister.
He said: “Peace comes through strength.
“With a more aggressive Russia and a more autocratic China, I pledge to increase the proportion of our GDP we spend on defence.”