Campaigning for Britain's tight referendum on leaving the European Union stepped up Saturday as Prime Minister David Cameron hammered home the economic impact of Brexit.

Cameron, fighting for his political future in the June 23 referendum which polls suggest is neck-and-neck, said Britain could slip into recession if it votes to withdraw from the European bloc.

Meanwhile Jeremy Corbyn, leader of the main opposition Labour party, made one of his highest-profile appearances of the campaign at a rally in central London.

Though Cameron and Corbyn are arch rivals, both want Britain to remain in the EU and are part of a campaign which has united most of the country's biggest political figures.

Pro-leave campaigners like former London mayor Boris Johnson, argue that Britain could thrive outside the 28-nation bloc, free to negotiate its own trade deals and with businesses liberated from red tape.

Grassroots campaign events were also taking place across Britain.

The official "In" campaign said it was holding over 1,000 events Saturday while a wave of anti-EU rallies were also taking place as campaigning cranks up after local and regional elections last week.

With less than six weeks to the vote, the "Remain" and "Leave" camps are tied at 50 percent each, according to the What UK Thinks website's average of the last six opinion polls.

The campaign has caused bitter divisions among Cameron's ruling Conservative party, over 100 of whose 330 lawmakers want to leave the EU.

Analysts suggest the premier would be forced to resign if he lost the referendum.

- It's the economy, stupid -

After a week of warnings from institutions like the Bank of England and the International Monetary Fund about the impact of Brexit, Cameron said Britain could face recession if it withdrew from the EU.

"If we vote to leave on June 23, we will be voting for higher prices, we will be voting for fewer jobs, we will be voting for lower growth, we will be voting potentially for a recession," Cameron said in a speech which he delivered standing on a pallet in his constituency west of London.

The prime minister said earlier that infrastructure projects like rail links would be hit by EU withdrawal as Britain would lose billions of pounds it receives from the European Investment Bank.

But Johnson, the most high-profile anti-EU figure and a Conservative, argued Britain could "flourish as never before" if it leaves, in a speech in Bristol, southwest England.

"This is not just the time to unshackle Britannia from her chains -- though it certainly is -- it's a time to speak up for freedom across the whole continent," said Johnson.

"If we vote on June 23 and take back control of our country, our economy and our democracy, then we can prosper and thrive and flourish as never before."

Corbyn, a veteran socialist deeply critical of the EU throughout his career, has been urged by some in his party to do more for the "Remain" campaign.

He responded with a speech Saturday which distanced Labour from Cameron but argued that issues like workplace protections and pollution should be addressed from inside the EU.

"Walking away won't solve the issue," Corbyn told a crowd of Labour supporters. "We're promoting unity, we're promoting internationalism, we're promoting social justice." AFP