Jeremy Corbyn will promise that a Labour government will "put the interests of the majority first" and oppose the "cosy cartel" running the UK as the left-wing leader delivers his first major speech of the general election campaign on Thursday (20 April).

"They say I don't play by the rules – their rules. We can't win, they say, because we don't play their game," he will tell an audience in Westminster, London.

"They're quite right. I don't. And a Labour government elected on 8 June won't play by their rules.

"These rules have created a cosy cartel which rigs the system in favour of a few powerful and wealthy individuals and corporations. It's a rigged system set up by the wealth extractors for the wealth extractors."

Corbyn, who plans to namecheck Southern rail, Arcadia boss Sir Philip Green and Sports Direct founder Mike Ashley, will vow to "overturn the rigged system".

"The Conservatives will use all the divide-and-rule tricks of the Lynton Crosby trade to protect the wealth extractors' rigged system," the Labour leader is expected to say.

"If I were Southern rail or Philip Green, I'd be worried about a Labour government. If I were Mike Ashley or the CEO of a tax-avoiding multinational corporation, I'd want to see a Tory victory. Labour is the party that will put the interests of the majority first."

The address will come just a day after MPs backed Theresa May's call for a snap general election on 8 June, more than a month after the local and metro-mayoral elections on 4 May.

The UK prime minister, who until very recently opposed holding a general election, said that the vote is necessary to strengthen her position at the Brexit negotiating table.

"Every vote for the Conservatives will make it harder for opposition politicians who want to stop me from getting the job done," she said. "Every vote for the Conservatives will make me stronger when I negotiate for Britain with the prime ministers, presidents and chancellors of the European Union.

"Every vote for the Conservatives means we can stick to our plan for a stronger Britain and take the right long-term decisions for a more secure future."

The latest opinion polls from ICM, YouGov and ComRes gave the Conservatives a 21-point lead over Labour, suggesting May could secure a majority of around 100 seats in the House of Commons.