Staff at Soho production company, MJZ, filmed the pair engaged in some nookie on Wednesday afternoon and then posted the video on You Tube.
The 'Sex and the City' clip has received thousands of hits on the video sharing site and has been viewed by people in Australia and New Zealand.
A producer at MJZ said she was shocked to look out from her 2nd floor window and spot the pair engaged in their sunshine romp.
She said: "I was working away and looked up and saw this bloke and a girl in the doggie position going at it on top of a building across the road.
"I couldn't believe it, I started laughing and shouted to a couple of my colleagues and then one of the girls grabbed a camera and began filming it.
"They were going at it for a good ten minutes but stopped a few times in between for a well earned break."
During the 30-second clip a male voice says "this is insane" before a female screams "how can they not think everyone's looking?"
The MJZ staffer added: "It was brilliant afternoon entertainment but I bet they are regretting it now. They are the laughing stock of London."
TV director Matt White was among the hundreds who forwarded the video on to pals.
He said: "You can't go out on a building in central London and do that and think no one is going to spot you.
"I reckon they have a career in porn films ahead of them."
It is believed the pair were on top of the Windmill Theatre building in Great Windmill Street but their identities are unknown.
Last night The Windmill International, an upmarket table top dancing club in Great Windmill Street, denied their staff were involved in the randy video.
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