Mr McCann said it may have been an "act of madness"

The father of Madeleine McCann has made a direct appeal to her kidnapper to come forward and begged: “It is not too late to do the right thing.”

Gerry McCann made the desperate plea as the police investigation showed no sign of a breakthrough.

The cardiologist and his wife Kate, both 39, are convinced their four-year-old daughter was snatched from her bed in the Algarve resort town of Praia da Luz as they ate at a restaurant nearby.

Writing in his daily blog, he insisted whoever was responsible for her disappearance must be suffering guilt and torment over what they have done.

The devout Catholic said: “We do not know who has taken Madeleine or why. Sometimes people do things for reasons that even they cannot understand.

“An act of madness, an accident or sudden impulse can lead to consequences that people may never have imagined or intended.

“Faced with such a situation we believe any human soul will ultimately suffer torment and feelings of guilt and fear.”

In a highly charged appeal, he said: “If you have done something you regret, if you find yourself in a situation you never intended, it is not too late to do the right thing.

“Please come forward, return Madeleine, leave her in a place of safety. At the very least, help us by letting us know what has happened to our beautiful little girl.”

Throughout their high profile campaign to find their daughter, the couple, from Rothley in Leicestershire, has avoided making direct contact with her abductor.

It has been 119 days since she disappeared and Mr McCann has become increasingly frustrated by the apparent lack of progress in the case.

Detectives in Portugal are still waiting for the results of DNA samples being analysed by the Forensic Science Service in Birmingham.

Speculation about what may have happened to Madeleine has been rife and several Portuguese newspapers have turned their attention to the couple themselves.

The McCanns' spokeswoman Justine McGuinness dismissed the latest claim that Portuguese police are examining a syringe and tranquillisers found in the family’s apartment.

She said: "I can categorically say the McCanns did not have syringes or sedatives with them on holiday. They do not use sedatives on their children."

Today will be another painful milestone for the family – it should have been Madeleine’s first day at school.

A desk, coat peg and locker have been set aside for the little girl at Bishop Ellis Catholic primary school in Thurmaston, Leicestershire, in case she is found.

Headteacher Gail Neill will say a special prayer to remember the missing girl.

She said: “We are deeply saddened that we cannot yet welcome Madeleine. A place has been prepared here for Madeleine, in exactly the same way as it has been for the other children.

“It will remain ready and waiting as we continue to pray, along with her parents, in the hope of her safe return to her family.”

The McCanns are expected to return to the UK in the next couple of weeks after spending just over four months in Portugal.

The lease on the villa they have rented in Praia da Luz runs out in mid-September.

Family members, who have travelled back and forth to the Algarve to help the couple, will help with the painful transition.

Both parents have spoken of their pain at arriving in Portugal as a family of five but leaving as a family of four.

Mr McCann will return to work at Glenfield Hospital in Leicester, while Mrs McCann will stay at home to look after two-year-old twins Sean and Amelie.

Spokeswoman Ms McGuinness said : “Kate’s priority at the moment is to be a mother.”