LONDON, April 15 (Xinhua) -- Britain's European Union (EU) referendum campaign formally kicked off Friday as leading political figures and campaigners reached out to different parts of the country to woo voters.

Friday marked the beginning of the official 10-week campaign for the EU referendum, which is scheduled to be held on June 23.

Two opposing campaign groups, "Vote Leave" and "Britain Stronger in Europe", have been designated as official campaigns for the referendum.

On Friday, both groups unveiled their statistics-packed video advertisements to highlight their cases, with leading politicians making high-profile speeches to set the tone for their campaigns.

Alistair Darling, a former Chancellor of the Exchequer, sent out a string of warnings against British exit from the EU at an event hosted by "Britain Stronger in Europe" in London.

"They are offering a fantasy future where we keep all the benefits of being in Europe without being part of the single market. It's Project Fantasy," Darling told his audience.

Leader of the Labour Party Jeremy Corbyn also made his first major intervention in the EU referendum debate on Thursday, urging voters to back continued membership in the bloc.

In a speech in central London, Corbyn said: "Labour is convinced that a vote to remain is in the best interests of the people of this country."

However, London mayor Boris Johnson, a vocal opponent of the EU, said that voting to quit the EU is a "vote for freedom" and that the day after the referendum will be "Independence Day".

"Would we now join a club that cost us 20 billion gross and 10 bn net? Which takes away the right to control our borders and our democracy?" he said Friday at a political rally in Manchester.

"The EU, they say -- it's crap but we have no alternative ... well we do have an alternative, and it is a glorious alternative," he added.