Comedian Russell Brand, who has previously urged people not to vote, has thrown his weight behind Labour.
Aside from endorsing Green candidate Caroline Lucas in Brighton, he said people outside Scotland had "got to vote Labour".
Scottish voters, he said, "don't need an English person telling you what to do".
Brand's comments follow an interview with Labour leader Ed Miliband - which David Cameron described as "a joke".
But Brand hit back that there was nothing funny about what the Tories have "been doing to this country"
Brand gave his endorsement on his YouTube Channel The Trews following an interview with Mr Miliband, among other politicians, in his east London home.
He accepted he had been "Mr Don't Vote", but stressed: "What I heard Ed Miliband say is if we speak, he'll listen, so on that basis I think we have got no choice but to take decisive action to end the danger of the Conservative Party.
"David Cameron might think I'm a joke, but I don't think there's anything funny about what the Conservative Party has been doing to this country - and we have to stop them.
"If you're in Brighton, I think it would be a travesty if we lost the voice of Caroline Lucas in Westminster, but anywhere else you have got to vote Labour.
"We have got to get the Conservative Party out of government in this country so that we can begin community activism, so we can be heard continually."
End of a revolution?
Mr Cameron has said he "did not have time to hang out" with Mr Brand, a comedian and actor, who has become a high-profile, alternative voice on the political scene.
The celebrity has campaigned against inequality, benefit cuts and corporate tax avoidance, and has spoken up on behalf of the rights of housing tenants.
Online reaction: "Sell out!" "Finally!"
Russell Brand's U-turn was heralded on Twitter as brave and honourable almost as quickly as he was branded a hypocrite and a sell out - but more importantly, hasn't he left it a bit late? After all, the deadline for registering to vote was a fortnight ago... Read more.
The former drug addict has also called for a new approach to drug taking, which he says should be treated as a health, rather than a criminal, matter.
He resigned from his BBC Radio 2 programme in 2008 after he and fellow presenter Jonathan Ross made obscene comments in prank calls to actor Andrew Sachs.
In a 2013 Newsnight interview with Jeremy Paxman, Brand said he had never voted because of "absolute indifference and weariness and exhaustion from the lies, treachery and deceit of the political class".
In the same interview, the actor called for people to shun the ballot box and pursue a "revolution" against the political elites.
He was heavily criticised for his non-voting stance from across the political spectrum, and his latest intervention comes two weeks after the deadline to register to vote on 7 May.
A full list of candidates standing in Brighton Pavilion can be seen here.
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