A secret library of over a hundred songs recorded by Michael Jackson could be released following his death.

One of the singer's biographers, Ian Halperin, claimed that the unheard songs had been made for his children.

Mr Halperin, author of Unmasked, The Michael Jackson Story, said before his death: “He wants to leave them for his kids, a very personal legacy to them. I was told he will not let them come out now.”

Jackson leaves three children: Prince, 12, Paris Katherine, 11, and Prince Michael II aged seven.

Times Archive 1972 The Jackson Five live at Wembley

Michael Jackson's twinkling feet scarcely seemed to touch the stage

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It is rumoured, given the parlous financial situation of his estate, that any such recordings will not be kept private for long. It is understood that Jackson may have gone to the grave under debts of about $400 million (£240 million) – though some believe the true figure may be much higher.

Sales of Michael Jackson’s music and memorabilia have already begun to soar. In America, the Thriller album is number one on iTunes, while his Number Ones album has now reached the top spot on the UK iTunes chart.

Online retailers Amazon say that Jackson’s albums had taken 14 of the top 20 places on the Amazon.co.uk sales chart. The Amazon chart was topped by his first solo album, Off The Wall, which features tracks such as "Don’t Stop ’Til You Get Enough" and "She’s Out Of My Life".

Already, Jackson’s death is beginning to producing a new industry. Outside the Los Angeles hospital where he was pronounced dead, a group of men appeared selling $10 T-shirts with a silhouette of Jackson and reading: “In loving memory of Michael Jackson.” Memorial T-shirts were also being sold at the Glastonbury music festival.

On eBay, bidding grew on a number of Jackson memorabilia items. Limited edition records, musical instruments used by the star and even a movie contract with his signature were being sold for thousands of pounds.

The Neverland ranch and Jackson’s final resting place, if made accessible to the public, could also become lucrative tourist attractions.

Graceland, the mansion owned by Elvis Presley and where he was buried, has become a much-visited landmark. Opening its doors to the paying members of the public is thought to have made the trust that operates Graceland in the region of $100 million.

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