Boris Johnson
Foreign secretary Boris Johnson. Reuters

British Foreign Secretary Boris Johnson has fuelled speculation that he hopes to eventually succeed Prime Minister Theresa May by spelling out his Brexit goals days before her major policy speech on the topic.

Johnson, a former journalist, wrote a 4,000-word article in the Saturday edition of The Daily Telegraph newspaper to explain how Brexit can bring a "glorious" future to Britain and help it become "the greatest country on Earth."

He says Britain shouldn't seek to stay in the European Union's single market or the customs union, and should seize the opportunity to make its own way.

The timing of his Brexit broadside is important because May is scheduled to detail her own Brexit views at a much-touted speech in Italy on 22 September.

Johnson making his own views known first may be seen by many as a challenge to her authority, which has been weakened by a poor result in the 8 June election that cost her Conservative Party its majority in Parliament.

Johnson sought to quiet speculation later Saturday by tweeting: "All behind Theresa for a glorious Brexit."

Johnson was an avid campaigner to have Britain leave the EU in the 2016 Brexit referendum.

He used the newspaper article to again raise the widely discredited idea that leaving the EU could allow Britain to add 350 million pounds ($475 million) a week to the National Health Service and argued that lifting regulations and reforming tax rules would allow Britain to prosper.

May has been able to hold onto her job despite her poor electoral performance, but has been facing increasing pressure as Brexit negotiations with the EU have stalled over the question of how much Britain must pay to leave the 28-nation bloc.

The Daily Telegraph later reported that Cabinet ministers Michael Gove and Priti Patel - who led the anti-EU Leave campaign - were backing Johnson's latest proclamations.

On Sunday (17 September), UK home secretary Amber Rudd in an interview with the BBC's Andrew Marr slammed Johnson for 'back seat driving' the Brexit talks.

"I have the great good fortune to work with Boris," Rudd continued.

"I know what an irrepressible enthusiast he is about Brexit and what he has done is set it out there - I think it's fine and I would expect nothing less. I don't want him managing the Brexit process. What we have got is Theresa May managing that process, driving the car to continue the allegory."

Labour Party leader Jeremy Corbyn, whose opposition party fared well in the general election, said on Saturday (16 September) through a spokesman that Johnson's Brexit views exposed the deep rifts within May's Conservative government.

"Boris Johnson has laid bare the conflicts at the heart of Theresa May's government over Brexit and cut the ground from beneath the prime minister's authority," Corbyn's spokesman said.

"In the process he has exposed the Tories' real Brexit agenda — a race-to-the-bottom in regulation and corporate tax cuts to benefit the wealthy few at the expense of the rights of the rest of us."