Facing steep odds and low popularity ratings, Britain's main opposition leader launched his election campaign on Thursday, painting himself as a populist outsider who will overturn a "rigged" political and economic system.

Labour Party chief Jeremy Corbyn said the June 8 election pitted "the establishment vs. the people" and insisted the result is not a foregone conclusion.

Labour trails a long way behind Prime Minister Theresa May's Conservatives in opinion polls, and many within the party believe 67-year-old socialist Corbyn is too left-wing to connect with voters.

Bookmaker Ladbrokes gives Labour 12-1 odds of winning the snap election called by May this week. Polls suggest the party could lose dozens of their current 229 seats in Parliament. The Conservatives currently hold 330 of the 650 seats.

In his first major speech of the campaign, Corbyn echoed anti-establishment sentiment that has upended politics from the United States to France.

To a crowd of supporters and journalists in London, he said that the old rules drawn up by political and economic elites no longer apply.

"I don't play by their rules, and if a Labour government is elected on the 8th of June we won't play by their rules either," he said.

"They are yesterday's rules, set by failed political and corporate elites we should be consigning to the past."

Corbyn made little mention of the biggest issue overshadowing the election — Brexit.

Britons voted by 52-48 percent in June 2016 to leave the European Union, and May says re-electing her with a bigger majority will strengthen the U.K.'s hand in divorce negotiations with the bloc.

The issue presents problems for Labour. The party backed remaining in the EU, but many of its legislators represent working-class areas of northern England that voted to leave.

Corbyn tepidly backed "remain" after decades of criticizing the bloc for giving too much power to corporations over workers.

He said Thursday that the election was about "what kind of country we want to have after Brexit." He said Labour respects the referendum result but will ensure EU-enforced workplace rights and environmental protections are not watered down after Britain leaves the bloc.