Jeremy Hunt has said fighting a general election would be "catastrophic" for the Conservative Party, should it fail to deliver Brexit.
The foreign secretary made on the comments on ITV's Peston as the prime minister spent the evening in Brussels trying to convince MPs to back her bid for a Brexit extension.
Mr Hunt said: "It would be absolutely catastrophic to for us to face the people again in a general election, which was our central promise."
He admitted the party has "got to turn around" its average voter age, which according to recent statistics has risen to on average be people above the age of 51.
He blamed a hung parliament for the delays in passing key legislation on the EU's departure from the European Union, adding he believes nobody is more committed to deliver Brexit than Theresa May.
Mr Hunt added a Brexit deal could be changed at a later date, not ruling out doing so if he become the next Tory leader.
Labour's shadow chancellor John McDonnell followed Mr Hunt, hitting back at his comments he wouldn't endorse any agreements made on Brexit should he win a leadership contest.
Mr McDonnell said: "One of the key issues for us in the discussions, the agenda included for us how do we entrench any agreement that we achieve."
He went on to add: "Clearly our big worry is if we can make a deal with Theresa May, what happens when she goes?"
The shadow chancellor said it undermines the faith people and his party have in the talks. He said the party had been looking at what legislation would be required to ensure a deal would stick and couldn't be scrapped by a new Conservative leader.
ITV News Political Correspondent Daniel Hewitt pointed out it looks as though the cross-party talks are floundering before they've properly set sail.
Mr McDonnell went on to say his party is willing to get around the table at a later date this week to further negotiate a Brexit deal both sides of the Commons can agree on.
He criticised Mrs May's attempts to agree on a deal. He hit out at key Government figures for saying a deal could be ripped up.
"This is the problem we've had for two years now," he said.
Mr McDonnell opened his diary to Number 10 for more talks.
He believes more were due to be held between officials on Thursday, stating: "We're available whenever. We trying to be completely open minded, we want to be as constructive as we possibly can.
"I think there is the potential of a deal but so far we've still got some fundamental disagreements about the nature of our future relationship with Europe."