Whisper it: the Godfather of Heavy Metal is turning down the sound. Lemmy from Motorhead, rock 'n' roll's king of speed, with his infamous weakness for amphetamines, an autobiography called White Line Fever, and claiming more than 2,000 notches on his bedpost, is slowing down the pace.

In two months' time, on Christmas Eve, Ian Fraser "Lemmy" Kilmister, known for album titles such as Overkill, Bomber and Everything Louder than Everyone Else, will be eligible to collect his free bus pass.

Thirty years after the band released the pulsating heavy rock classic "Ace of Spades", Lemmy has re-recorded the song at half the tempo as a blues number – and sanctioned it for a commercial.

After the painful sights of Johnny Rotten in a tweed jacket advertising butter and Iggy Pop flogging insurance, television viewers will get to make up their minds on the new, languid version of "Ace of Spades" this Sunday. Lemmy will be seen supping a glass of French lager instead of his usual Jack Daniel's, as part of an advertising campaign for Kronenbourg 1664 titled "Slow Down the Pace". The track, on which Lemmy plays harmonica, will be made available for download from the beer brand's website.

"Ace of Spades" has not been re-recorded before. It features Lemmy's two Motorhead bandmates, Phil Campbell and Mikkey Dee, who both appear in the TV ad jamming in a bar close to Lemmy's home in Los Angeles, but which has been dressed to give the impression of rural France.

Matt Doman, creative director at the advertising agency BBH, admitted Lemmy "was quite challenging but really because he's very protective of the track. We spent a rollercoaster of a day with him in the recording studio."

At the start of November, Motorhead will touch down in Britain as part of a (non-acoustic) international tour. This Saturday, at the National Film Theatre in London, a documentary about his life will get its UK premiere at the London Film Festival. Lemmy, which took three years to make, celebrates the rocker's daily consumption of two packets of Marlboro Reds and a bottle of Jack Daniel's. In the film, the Foo Fighters frontman, Dave Grohl, makes the observation: "More than any other rock musician, he's the baddest motherfucker in the world." In heavy metal circles, that is praise.