It is the haunting rendition of Auld Lang Syne sung to Burns's intended tune that has had Sex and the City film audiences the world over brushing away tears.

Now, thanks to the power of Hollywood and the internet, the song is making unexpected stars of a husband-and-wife folk duo from Edinburgh.

Mairi Campbell and Dave Francis, who together form The Cast, recorded their Auld Lang Syne for Culburnie Records 14 years ago and did not know it was to feature in the film event of the year until after the premiere.

But the song, which plays for more than three minutes over the emotionally charged New Year scene in the movie, has become an internet sensation. Although the words are familiar, the tune is not the well-known version, but the more soulful melody Robert Burns originally had in mind.

It has been played more than 26,000 times on YouTube since it was uploaded a week ago.

Comments by fans, many of who admit the song made them cry, include, "This is one of the most beautiful things I've ever heard". On Apple iTunes, it is by far the most popular of the 150 Auld Lang Syne versions listed.

Ms Campbell, 42, said: "I really like the fact that it's associated with the film because of the way it's been used. It's great for folk music to be in a cool place."

Mr Francis, 53, added: "I hope that it will make our music heard. All any musician wants is to be heard."

The couple, who have been playing and writing songs together for 17 years and have three albums, said they were still getting used to the song's popularity.

Mr Francis said: "I don't think we'd quite appreciated the scale of the phenomenon that is Sex and the City."

The Cast's Auld Lang Syne plays over a montage of images of the main characters at New Year.

Mr Francis said: "It's an unexpected juxtaposition because Sex and the City is a very contemporary context and here you have this beautiful poem written by an 18th-century Scottish rural poet and songmaker, and you'd think they'd be diametrically opposed.

"But there's something in the meaning of the song that transcends those differences. It's the original tune Burns would have had in mind. They do four out of the five verses, so it's a good blast of Scots in the middle of this sharp contemporary context."

The couple do not know how their song came to the film producer's attention. One theory is that Sarah Jessica Parker may have been in the audience of the Kennedy Centre Awards in 1999 when The Cast played the song for Sean Connery.