Scotland Yard forensics want to use new ­techniques to analyse the curtains, which hung in the room where Madeleine was sleeping with her baby brother and sister

Detectives plan to do new tests on curtains which hung in the apartment where Madeleine McCann disappeared.

They believe the fabric, which has been sealed in an evidence file since three-year-old Madeleine vanished in Portugal in 2007, may hold DNA which will identify to her abductor.

Scotland Yard sent an urgent request to their counterparts in Portugal asking permission to re-examine the fabric.

Forensic experts on the Operation Grange team want to use new ­techniques to analyse the curtains, which hung in the room where Madeleine was sleeping with her baby brother and sister.

Officers are also set to re-examine 30 strands of hair found in the apartment in the Ocean Club resort in Praia da Luz using advanced genetic and biological testing procedures. 

A team led by Det Chief Insp Andy Redwood has asked for a quick response to the request.  

They think the curtains from apartment 5A will have been preserved well enough to hold traces of DNA from Madeleine’s captor.

Portugal’s Public Ministry will now decide if they are willing to hand over the material, which is being kept at the National Institute of Forensic Medicine in the city of Coimbra.

There have been significant new developments in DNA science since the initial investigation in 2007.

The first murder conviction using DNA evidence was in 1988, when baker Colin Pitchfork was found guilty of killing Lynda Mann and Dawn Ashworth, both 15, in Narborough, Leics.

Since then the UK has developed one of the largest “libraries” of DNA samples, which increases by more than 400,000 profiles every year.

DNA samples can be taken from body fluids, but also from tiny quantities of human cells left on any surface, from cups and cutlery to cigarette ends.

The increase of DNA samples being taken and stored has led to a rise in convictions, especially for crimes committed a number of years ago.

The quality of DNA can now be ­“amplified” using complex chemical processes.

A sample of DNA can also now be extracted from a single cell and laboratory robots are being used to speed up the process.

Last week Francisco Brizida, president of the Institute of Legal Medicine and Forensic Sciences, where the DNA library is held, said: “Technology now allows us to go further than years ago.”

But he said: “I wouldn’t like to be that ambitious and say the secret to unlocking the Madeleine McCann case lies in our lab.”

A Portuguese police source said: “The best hope is to pass the sample to British officers.”

Police digs in Praia da Luz and interviews with new suspects this summer ended in disappointment.

The probe run by 30 officers in Operation Grange has cost £10million.