LONDON - Former British Foreign Secretary Boris Johnson called on Prime Minister Theresa May to rip up her Brexit proposals, ratcheting up the pressure on May as she prepares to face her divided party at its annual conference in two days time.

"This is the moment to change the course of the negotiations and do justice to the ambitions and potential of Brexit," Johnson wrote in Friday's Daily Telegraph, adding a six-point alternative plan for Brexit.

"There has been a collective failure of government, and a collapse of will by the British establishment, to deliver on the mandate of the people," he wrote.

Just six months before the United Kingdom is due to leave the European Union on March 29, 2019, little is clear: PM May has yet to clinch a Brexit divorce deal with the EU and rebels in her party have threatened to vote down any deal she makes.

Johnson, one the most prominent campaigners for Brexit in the 2016 referendum, resigned in July as foreign secretary over May's Brexit proposals which he cast in his 4,600-word Daily Telegraph article as "enforced vassalage".

May has repeatedly said her Brexit proposals are the only viable ones.

Reuters