The Chancellor said he would publish “updated analysis both of the deal that is being proposed and of the counterfactual no-deal situation”.
No 10 faced fierce criticism when, in August, it suggested parliament would be shown economic forecasts “just on the deal” that the prime minister hopes to strike.
One pro-EU Labour MP accused Ms May of refusing to let MPs “see the gory details for themselves before deciding whether or not to jump off the cliff edge”.
But Mr Hammond, speaking ahead of his conference speech and an attempt to rebuild battered Tory links with business leaders, insisted parliament would be given full information.
“We have made a commitment that – once we have a deal to put to parliament and we are starting the debate that will lead to a meaningful vote in parliament – we will then publish updated analysis both of the deal that is being proposed and of the counterfactual no deal situation,” he told BBC Radio 4.
Significantly, the Chancellor said he believed the Treasury’s initial forecast about a no-deal Brexit – predicting a 7.7 per cent hit to GDP and an £80bn hole in the public finances – would “not have changed radically”.
Mr Hammond has also warned that crashing out of the EU would trigger further spending cuts – just as more Tories urge him to end the pain of austerity.
However, in the interview, he insisted that preventing Northern Ireland leaving the UK’s customs territory – threatened by the “backstop” demanded by the EU – would be worth the damage of a no-deal Brexit.
“If the EU put to us a proposal for a deal that would involve us accepting the break-up of the UK then I would readily accept that no deal would be a better outcome than that,” he argued.
Mr Hammond dismissed calls by Boris Johnson and other Brexiteers for a ‘Canada-style’ trade deal, because Brussels had insisted it would only be possible by leaving Northern Ireland aligned with the EU.
“When you go into a negotiation you have to understand the position of the people you're negotiating with," the Chancellor said. “It's no good just ignoring it and banging your head against a brick wall.
“You have got to understand what their red lines are as well so you can try and find a landing ground you can both accept, which means a deal gets done.”
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies