Private investigators searching for Madeleine McCann mounted a surveillance operation amid fears that she was being held prisoner in a run-down farmhouse, secret police files reveal.

They acted after a British holidaymaker spotted a ‘gaunt’ blonde girl wearing a black wig being dragged by ‘gipsy women’ 30 miles from where Madeleine was snatched.

Jean Godwin, 56, a retired care home worker, said the girl she saw on the Algarve was ‘100 per cent Madeleine McCann’

Seen with a girl: McCanns’ investigators believe Yvone Albino, a cleaner from Silves, was seen outside the McCanns’ apartment in May 2007

One of the women spotted in Carvoeiro by Mrs Godwin was seen by another British tourist acting suspiciously outside the McCanns’ apartment on the day the youngster vanished from Praia da Luz.

The evidence prompted investigators to follow their suspect to an isolated farmhouse in an orange grove near the town of Silves, north of Portimao. In the following months she paid several visits to the property, a holiday home owned by a teacher and his partner whom the inquiry team deemed to be ‘suspicious’.

Their concerns were raised when they discovered a white Citroen Berlingo with a child’s doll on the back seat and a child’s drawing among rubbish bags – even though the couple did not have young children.

Investigated: Jorge Martins and partner Maria Silveira had their remote home checked

They also spotted the man buying clothes suitable for a girl of five – Madeleine’s age at the time. But surveillance was eventually wound down and the child was never found.

The operation began in 2008 after Mrs Godwin, from Widnes, Cheshire, rang the ‘Find Madeleine’ hotline and gave her suspicions to private investigators. By this stage, the official police inquiry into the disappearance on May 3, 2007, had been closed.

Madeleine’s parents Kate and Gerry continued to employ private detectives in the hope of finding their daughter but these investigators have no legal powers to force suspects to talk to them. The sightings were passed to the Portuguese police who deemed them irrelevant and promptly archived the reports.

Details of the evidence are contained in a 2,000-page police dossier finally published by the Portuguese authorities after requests from newspapers including the Daily Mail. It contains the testimony of Mrs Godwin, who claims she spotted Madeleine in September 2008.

She said: ‘This was a young girl, in the middle of the two women and holding the hand of each. Her eyes were wide open and my attention was drawn to the large irises.

‘The child was wearing what was clearly a black wig. It was short, cut in a bob style and very thick. The wig was shiny and unnatural looking and out of keeping with her very pale complexion and fair eyebrows.

‘I would say she was about 3ft 1in tall and about five years of age. She was very thin and I would describe her as malnourished. Her cheeks looked gaunt. I think she had a bump on her nose.

'I am convinced that the little girl I saw that morning was Madeleine. I have been asked how certain I am. I will say I am 100 per cent sure.’

Mrs Godwin described the first woman as being an ‘obese’ size 30, in her mid-to-late 40s with ‘dirty and unkempt’ red hair. The second woman was around 60, with unwashed brown hair, and even fatter.

The McCanns’ investigators believe the red-haired woman was Yvone Albino, a cleaner from Silves. Another witness, Jeni Weinberger, from Salisbury, Wiltshire, said she saw a woman resembling Mrs Albino outside the McCanns’ apartment in May 2007.

Mrs Albino, who has two grown-up sons, met teacher Jorge Martins and his partner Maria Silveira at their house in the orange grove.

David Edgar, a private investigator working for the McCanns, described their movements as ‘suspicious’.

Portuguese police confronted Mrs Albino, who said she knew nothing about either sighting and denied any contact with young children. Officers found the house deserted. The woman with Mrs Albino in Carvoeiro was never identified.

Mr Martins and Miss Silveira have never been accused of any crime by police. He told police the doll was given to him by his students several years earlier.

The McCanns’ spokesman Clarence Mitchell said: ‘It’s clear that our investigators have made considerable efforts to follow up leads but without having full access to the files and co-operation from the Portuguese police.’