Mr Hammond says "national interest trumps the party interest" and vows to "act in what I believe is the best interest" of the UK.
Chancellor Philip Hammond has suggested he could try to bring down the government to block a no-deal Brexit.
In an exclusive interview with Sky News, he left open the option of backing a no-confidence vote against the next prime to stop them pursuing something "not in Britain's interests".
Mr Hammond admitted it is not a move he would make "lightly or enthusiastically", but warned that "national interest trumps the party interest".
Tory MPs vying to replace Theresa May have been jockeying over whether they would ensure the UK leaves the EU on 31 October regardless of whether or not parliament passes a withdrawal agreement.
Three former cabinet ministers have committed to doing so - Esther McVey, Dominic Raab and Boris Johnson.
Mr Hammond said he was meeting all the candidates this week to decide who to back.
"I would not support a policy of no-deal by choice," he told Sky News.
"That is not in Britain's interests, it would be taking huge risks with the unity of our country, with our security and clearly with our economy.
"I couldn't support a government policy stance that said as a matter of choice we are going to pursue a no-deal exit."
The MP who replaces Theresa May could be in power by the end of July
Asked if he would vote for or against the next government in a no-confidence vote if it pursued no-deal, Mr Hammond said: I've been in parliament for 22 years.
"I have never once voted against the Conservative whip, so it is not something that I would do lightly or enthusiastically.
"But I am very clear that the national interest trumps the party interest.
"And if I am presented with a difficult choice, I will act in what I believe is the best interest of this country."
Esther McVey, Dominic Raab and Boris Johnson all promised Brexit on 31 October
He previously told the BBC's Andrew Marr Show: "I don't want to have to start now contemplating such a course of action."
It comes after Commons Speaker John Bercow suggested MPs would thwart any plan by the next Tory leader for a no-deal divorce from the EU.
"The idea that parliament is going to be... evacuated from the centre stage of debate on Brexit is unimaginable. It is simply unimaginable," he said.
Britain is on course to leave the EU in five months' time, with the leadership contest for a new prime minister expected to wind up by the end of July.
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