The Times reports that the Chancellor gave a speech to civil servants last week making clear that he will oppose any move by the next Prime Minister to take Britain out of the EU without a deal.
Mr Hammond is said to have told staff: “It has not escaped my attention that the next Prime Minister’s majority will be only three, and that I will be a backbencher.”
He added: “Parliament is going to be where the action is, and I will be there on the backbenches.”
A source at the meeting meanwhile told the paper that the Chancellor received “a huge round of applause” after he urged Treasury officials not to change their advice to suit the next PM.
The intervention marks the latest warning from Mr Hammond about a no-deal Brexit.
Earlier this month, he told MPs that a disruptive split from the EU could cause a “hit to the Exchequer of about £90bn”, blowing a hole in both Boris Johnson and Jeremy Hunt’s spending plans.
In what could be his final stint at the Commons despatch box as Chancellor, Mr Hammond meanwhile said it would be a job for Parliament – of which he would “proudly” continue to be a member – to ensure a no-deal exit “doesn’t happen”.
And the Cabinet minister this weekend warned that Britain “can’t control” the impact of leaving the EU without a deal.