Labour ex-premiers Tony Blair and Gordon Brown issue stark warnings about no deal Brexit

Former prime ministers Tony Blair and Gordon Brown have issued a stark warning to the country's next leader about the potentially “catastrophic” dangers of a no-deal Brexit.

Tory leadership frontrunner Boris Johnson has promised to leave the European Union on October 31 come what may, even if that means leaving without a deal in place.

As the race for Number 10 enters its final stages, the Labour ex-premiers warned that a no-deal break from Brussels could be "catastrophic" or see the British economy “pushed off a cliff”.

Mr Blair said another referendum was the best outcome for former foreign secretary Mr Johnson.

He wrote in The Times: “Even before he becomes prime minister this week, Boris Johnson has boxed himself into a no-deal Brexit. If he doesn't back down from his stated negotiating position, he will fail."

He said the 2016 referendum gave the Government a mandate for Brexit, but not a no-deal scenario, Mr Blair claimed, and "crashing out without public endorsement would be a gargantuan risk".

"No-one knows with certainty the impact of no-deal for the simple reason that no developed nation has ever left overnight its preferential trading arrangements in this manner.

"It could be merely very difficult or it could be catastrophic."

If Parliament voted against a no-deal Brexit, Mr Blair said he did not believe Mr Johnson would push on regardless - meaning a referendum or a general election would be required.

Mr Blair said he could understand why Mr Johnson might push for a general election against Jeremy Corbyn, but that "ploy" would be "completely unjustifiable" because it would be about issues other than just Brexit.

"Brexit is an issue that stands on its own. It should be decided that way," Mr Blair said.

Neither Mr Johnson nor his leadership rival, Jeremy Hunt, have ruled out a no-deal Brexit if agreement cannot be reached with Brussels.

In his own warning, Mr Brown highlighted that polling suggesting support for a no-deal Brexit was declining.

Mr Brown said: "Boris Johnson is becoming prime minister just as support for his October 31 no-deal policy is falling away."

He added: "Already, away from Westminster, three million Brexit voters will not support a no-deal Brexit.

"Many more are ready to say 'no' to a no-deal and to seeing the British economy pushed off a cliff."

Additional reporting by Press Association.