LONDON -- The opposition Labour Party kicked off its campaign for Britain's December general election with one overriding message Thursday: It's not just about Brexit.

Labour leader Jeremy Corbyn put the emphasis firmly on economic and social issues, calling the Dec. 12 vote a once-in-a-generation chance to transform the country. All seats in the 650-seat House of Commons are up for grabs in the early election, chosen by Britain's 46 million eligible voters.

In his first stump speech of the six-week campaign, Corbyn said the left-of-centre party's plan would take on "vested interests" and "born to rule" elites -- a dig at Conservative Prime Minister Boris Johnson and his Conservative party's big-business backers.

"We're going after the tax dodgers. We're going after the dodgy landlords. We're going after the bad bosses. We're going after the big polluters. Because we know whose side we're on," Corbyn told supporters at a rally in London. "Whose side are you on?"

Johnson sought this election, which is being held more than two years early, to break the political impasse over Britain's stalled departure from the European Union. But Corbyn wants to shift the election battleground away from Brexit and onto more comfortable terrain: the many versus the few.

Labour is hoping that voters want to talk about issues such as health care, the environment and social welfare -- all of which saw years of funding cuts by Conservative governments -- instead of more Brexit debates.

For his part, Johnson plans to campaign as the Brexit champion, blaming Corbyn's "dither and delay" for the country's failure to leave the EU on Thursday as scheduled.

While the Conservatives have a wide lead in most opinion polls, analysts say the election is unpredictable because Brexit cuts across traditional party loyalties. For many voters, their identities as "leavers" or "remainers" are more important than their party affiliations.

A bill authorizing the early election was rushed through Parliament this week and officially became law Thursday when it received royal assent.

Sticking to his party's core issues, Corbyn on Thursday called out prominent business leaders -- including media mogul Rupert Murdoch and aristocratic landowner the Duke of Westminster -- as he painted Johnson's Conservatives as champions of the wealthy few.

Johnson once again banged the Brexit drum, ignoring his failure to get British lawmakers to pass his Brexit divorce deal and his previous vow to leave the EU by Oct. 31 "come what may." Earlier this week, the EU granted Britain a three-month Brexit delay, setting a new Jan. 31 deadline for the country to leave the bloc and imploring British politicians to use the extra time wisely.

"If you vote for us and we get our program through ... we can be out at the absolute latest by January next year," Johnson said Thursday as he visited a hospital.

Johnson also tried to steal some of Labour's thunder by promising more money for key public services such as hospitals, police and schools.

Labour is vulnerable over Brexit because the party is split. Some of its leaders, including Corbyn, are determined to go through with British voters' decision to leave the EU, while others want to remain. After much internal wrangling, Labour now says if it wins the election, it will negotiate a better Brexit divorce deal, then call a referendum that gives voters a choice between that deal and remaining in the EU. The party has not said which side it would support.

"The prime minister wants you to believe that we're having this election because Brexit is being blocked by an establishment elite," Corbyn said. "People aren't fooled so easily. They know the Conservatives are the establishment elite."

"Labour will get Brexit sorted within six months. We'll let the people decide whether to leave with a sensible deal or remain," he added.

Corbyn shrugged off suggestions that he is dragging down the party's popularity. Critics say the 70-year-old socialist is wedded to archaic policies of nationalization and high taxes, and accuse him of failing to stamp out anti-Semitism within the party.

Johnson's critics bash the 55-year-old for his long history of misrepresentations and broken promises, and a string of offensive comments that he has tried to shrug off as jokes.

"It's not about me," Corbyn said Thursday. "It's not a presidential election. It is about each and every one of us (candidates)."

Many British voters are fed up as they face the third major electoral event in as many years, after the country's 2016 EU membership referendum and a 2017 election called by Johnson's predecessor Theresa May to try to strengthen her hand in negotiations with the EU.

May's move was a spectacular miscalculation that cost the Conservative Party its majority in Parliament. She resigned after failing to get her Brexit deal passed by Parliament and Johnson took power in July.

More than three years after the Brexit referendum, Brexit positions have become entrenched and the debate has soured, with lawmakers on all sides receiving regular abuse online and in the streets. The toxic political atmosphere has prompted some long-time lawmakers to drop out of the race altogether, including Culture Secretary Nicky Morgan, a Conservative.

"Over the last couple of years, I have had to have a couple of people prosecuted for death threats," Morgan said. "I think there needs to be a wholesale culture change in the House of Commons. We've got to tackle this culture of abuse."

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An earlier version corrected the spelling of Corbyn in first sentence.