Out of the 432 human hairs that were collected by Portuegese investigators, 98 of these were not connected with a particular person.
British police are now campaigning to retest the hairs to discover who they belong to.
Madeleine McCann's parents Kate and Gerry hold up an aged image of their daughter
Improvements in technology mean that new DNA tests could hold the clue to the toddler’s disappearance, which at present remains unsolved.
Portugal’s top forensic centre boss said: ‘I can’t say for sure new DNA tests that didn’t yield a conclusive result in 2007 could now yield an objective result.’
CONVICTED PAEDOPHILE ARRESTED IN MALTA
‘But technology nowadays allows us to go further than years ago in areas like genetic markers.’
Maddy went missing from Portuguese resort Praia da Luz in May 2007, while her parents dined just metres away from the apartment.