A no-deal Brexit would betray Britain's decision to leave the European Union, former finance minister Philip Hammond said Wednesday, as he slammed Prime Minister Boris Johnson's "wrecking" approach to negotiations.

Hammond, who quit as chancellor just hours before Johnson took over from Theresa May on July 24, said there was no popular or parliamentary mandate for a no-deal Brexit, saying most people wanted an orderly exit from the EU. "No-deal would be a betrayal of the 2016 referendum result. It must not happen," he wrote in The Times newspaper.

He said it could turn Britain into "a diminished and inward-looking little England."

The British parliament three times rejected the withdrawal agreement May negotiated with Brussels, with many MPs troubled by the "backstop" - a mechanism that would keep the UK in EU customs arrangements to prevent a hard border on the island of Ireland.

Hammond said the shift of position from seeking changes to the backstop to demanding its removal "is a pivot from a tough negotiating stance to a wrecking one," setting an impossibly high bar.

"This is a demand the EU cannot, and will not, accede to.

"It's time for our government to demonstrate its commitment to a genuine negotiation with the EU to achieve a deal."

Britain is due to leave the European Union on October 31.

Johnson has pledged to stick to this date, whether a deal can be struck with Brussels or not.

Hammond said a no-deal Brexit would also threaten the United Kingdom's integrity as it risked collapsing the peace accords in Northern Ireland and triggering a referendum on the province leaving the UK and joining the Republic of Ireland, an EU member state.

It would also lead to a second secession referendum in Scotland and the likely break-up of the UK, Hammond claimed.

He also said US talk of a "great trade deal" meant a trade deal that was great for them, opening up Britain to US produce that would "destroy British agriculture."

Hammond warned that if parliament wanted to go down a particular route to prevent a no-deal Brexit, the means would emerge to allow that to happen.