Britain is on the verge of submitting proposals for a new deal to leave the European Union, according to Prime Minister Boris Johnson, even as France warned that a no-deal exit is the most likely outcome as the deadline looms.

Johnson told the BBC that his government would be making “a very good offer” to Brussels “very soon”, with just 30 days to go until the October 31 Brexit date.

He rejected reports it would see customs posts along the Irish border but conceded checks would be “just the reality” somewhere once Britain leaves the EU’s customs union and single market.

His Irish counterpart, Leo Varadkar, welcomed Johnson’s remarks disowning the customs posts plan, warning it would have been evidence of bad faith by London.

“No British government should seek to impose customs posts between Northern Ireland and the Republic of Ireland,” he told parliament in Dublin.

EU leaders, however, have complained they have yet to see a concrete alternative to the current divorce deal, as the government struggles to unravel four decades of European integration against a hostile, largely pro-EU parliament.

Johnson himself has been slapped down by the courts for unlawfully suspending parliament, where he has lost a wafer thin majority because of the divisive issue, giving him little room for manoeuvre.

In Paris, French Foreign Minister Jean-Yves Le Drian said a no-deal Brexit was still the “most plausible” scenario in the absence of any acceptable proposals from London.

Johnson is seeking to renegotiate the divorce terms struck by his predecessor Theresa May last year, which parliament rejected three times.

He is focusing on the so-called backstop plan intended to keep goods flowing freely between Northern Ireland and Ireland.

The backstop would keep Britain in the EU’s customs union to avoid border checks, perhaps indefinitely – something Brexit supporters would not accept.

The issue is contentious, as the removal of border posts was seen as key to bringing peace to Northern Ireland after three decades of sectarian violence between republicans and unionists that left thousands dead. (AFP)