A man in London had a lot of people doing a double-take when they spotted him playing his guitar while breezing down a busy highway.

A woman on a bus traveling next to the moving musician snapped a photo of him and posted it to Twitter.

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Soon, other people spotting the man playing his bass guitar behind the wheel, too, and posted pictures on their own social media.

"He was definitely playing the guitar and my first thought was: 'Oh my god, is he really doing that?'" Nichola Carr, who glimpsed the man.

"The children found it funny and would shout: 'Here comes the guitar man,' as he kept driving past," Carr continued, "It was a bit concerning."

Pictures show the man with one hand on the wheel, and the other on the neck of his five-string Warwick electric bass.

Safety experts warn that doing anything other than paying attention while driving is highly dangerous.

"We always say you cannot do two things at once if one of them is driving," stated Neil Greig, director of policy and research at the Institute of Advanced Motorists.

Witnesses to the driver's antics swiftly labelled him as "idiotic."

See picture here.