The parents of Madeleine McCann left behind their two-year-old twins, Sean and Amelie, yesterday and travelled to Rome to ask the Pope to pray for the return of their daughter.

As Kate and Gerry McCann left Portugal for the first time together since their eldest child disappeared 27 days ago, it emerged that the police had issued an incorrect description about the height of her possible abductor.

The mistake has led to many people in Praia da Luz assuming that the abductor is most likely to be a foreigner because the description is taller than the average Portuguese man.

A family source said: “The police have made a mistake. The description given was of a man who is 5ft 10in but they have somehow managed to get it wrong. The description given [by the witnesses] was 5ft 7in.

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“It seems the description was lost in translation. What has happened is that the police have given a description of quite a tall man when they should have been talking about someone who is relatively short. It is a big mistake and it is not good enough.”

The correct description appears in the Portuguese language appeal but most residents and holidaymakers in Praia da Luz are English and the media have followed the description in the English translation. Concerns have also been raised about police treatment of Madeleine’s favourite toy, a pink Cuddle Cat, which her mother, a locum GP, has kept with her ever since the little girl disappeared and carried with her on the plane to Italy. It is feared that the toy may have carried potentially useful DNA evidence that was not gathered in the early stages.

The McCanns believe that today’s general audience with Pope Benedict XVI could have a “huge bearing” on whether their daughter is returned.

The couple will have a few moments to talk to the Pope. Mrs McCann will give him a photograph of Madeleine and ask him to pray for her return.

Mr McCann said: “It is a huge privilege and means so much to us not only spiritually but because it could have such a massive impact on the chances of finding Madeleine.

“It’s difficult to have something bigger than this. It could have a huge bearing on whether we can get Madeleine back.”

Mr McCann admitted that he and his wife felt nervous but were determined to remain positive because the meeting could “make such a difference”.

Many of the thousands of people who will attend the general audience in St Peter’s Square are expected to wear the yellow and green ribbons that have become the symbol of the international campaign to find Madeleine. Mr and Mrs McCann will sit in the front row, known as the prima fila, which is normally reserved for visiting heads of state or other dignitaries. They will be among just 25 people introduced to the Pope and he is expected to mention Madeleine “prominently” in his prayers.

The couple, both 38, flew to Rome in a private jet lent by Sir Philip Green, the billionaire owner of Bhs and Topshop.

While the couple are in Rome their twins are being looked after by Mr McCann’s sister, Trish Campbell, and her husband, Sandy. Mrs McCann said: “Leaving them is really hard, I have never left them before. From a selfish point of view we would have liked to have had them here as a comfort. But I am sure it is not the best thing for them. This trip is about Madeleine.”

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