Spells out his Brexit goals days before May’s major policy speech on the topic

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.

Mr. 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 should not seek to stay in the 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 Ms. May is scheduled to detail her own Brexit views at a much-touted speech in Italy on September 22.

Mr. Johnson making his own views known before Ms. May’s speech may be seen by many as a challenge to her authority, weakened by a poor result in the June 8 election that cost her Conservative Party its majority in Parliament.

Mr. Johnson was an avid campaigner for leaving the European Union in the 2016 referendum.

Increasing pressure

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.

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

Deep rifts: Corbyn

Labour Party leader Jeremy Corbyn, whose party fared well in the general election vote, said through a spokesman that Mr. Johnson’s Brexit views exposed the deep rifts within Ms. May’s 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,” Mr. Corbyn’s spokesman said.