The theme song for the new James Bond movie, sung by Adele, has been leaked on the internet.

Adele confirmed on Monday that she had recorded the theme for Skyfall and posted a picture of the song credits on her official Twitter page.

However, the track wasn't due to be unveiled until 0.07 BST on Friday 5 October.

The same date marks the 50th anniversary of the release of the first James Bond film, Dr. No.

Some critics are saying the style of the leaked song reminds them of Dame Shirley Bassey, famous for Bond songs like Goldfinger and Diamonds Are Forever.

Adele's confirmation that she had done the song came after months of rumours.

Her photo on Twitter appears to show the cover page of the sheet music for the Skyfall theme.

It lists the composers as A. Adkins, the singer's full name, and P. Epworth - the producer and co-writer of her hit single Rolling In The Deep.

'77-piece orchestra'

The music has been arranged by Epworth and film composer JAC Redford, whose credits include The Help, The Iron Lady and Wall-E.

In a statement, Adele said: "I was a little hesitant at first to be involved with the theme song for Skyfall.

"There's a lot of instant spotlight and pressure when it comes to a Bond song.

"But I fell in love with the script and Paul (Epworth) had some great ideas for the track and it ended up being a bit of a no brainer to do it in the end.

"It was also a lot of fun writing to a brief, something I've never done which made it exciting. When we recorded the strings, it was one of the proudest moments of my life.

"I'll be back combing my hair when I'm 60 telling people I was a Bond girl back in the day I'm sure."

Skyfall was recorded at Abbey Road studios in London with a 77-piece orchestra.

Hints

Adele first hinted she would be working on the theme song during an interview on Jonathan Ross's chat show on ITV1 in September 2011.

"I'm going back in the studio in November, fingers crossed," Adele told Ross.

"Well this is actually a theme, what I've got to do for, um… Wow. That's really giving something away isn't it?"

Shortly after Adele's appearance on The Jonathan Ross show last September, her friend Tinie Tempah, said he'd spoken to Adele about her Bond recording.

Speaking at the Mercury Prize on 6 September last year the rapper said: "I was with her (Adele) yesterday, she was telling me about it and that's amazing.

"I've always wanted to do a Bond theme. I'm a bit jealous actually. No, let's leave it to her, it's always a really big diva that does it right?"

Recent Bond themes have met with a poor reception.

Chris Cornell's gritty You Know My Name, from Casino Royale, was described as "unexpectedly dull" and "forgettable"; while Jack White and Alicia Keys' duet Another Way To Die, from Quantum Of Solace, was branded "a missed opportunity".

Adele's theme is the first to carry the same name as the film since Madonna's Die Another Day in 2002.

The 23rd Bond film, Skyfall, is due for release on 26 October in the UK.