Portuguese police failed to record any of their interviews with McCanns

The admission has raised concerns about the accuracy of transcripts of interrogations conducted by detectives in the Algarve.

It will fuel fears that police could manipulate evidence contained in the interviews to frame the McCanns.

A source close to the couple said today: "There were no tape recordings of any of the interviews. It is just not routine in Portugal."

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Another source said: "When Kate and Gerry and their friends gave their statements, they had to give their evidence sentence by sentence. It was written down, translated and typed up line by line, retranslated and afterwards they had to agree it.

"If you think about it, they could have been mistranslated in a variety of ways. One word in English can have a subtly different meaning to Portuguese. You just don't know that what they actually wanted to say and what they were agreeing to is the same thing."

The Evening Standard has been told that Portuguese police did not record any interviews with the McCanns or their friends, who make up the Tapas Nine and whose evidence is critical in backing up Madeleine's parents' version of events - that the four-year-old was abducted from their apartment at the Ocean Club resort in Praia da Luz on 3 May.

By contrast, British police have recorded all interviews with suspects on tapes since the mid-Eighties when a series of miscarriages of justice - including wrongful convictions of the Birmingham Six and the Guildford Four - led to a root and branch change to the criminal justice system.

Taped evidence prevents police doctoring statements or forcing confessions under duress. Mrs McCann was interrogated for almost 15 hours over the course of two days with just a few hours sleep in between.

Police had tried to break her down, hoping she would confess to her involvement in Madeleine's disappearance, and there will be concerns that the written transcripts - unlike a taped interview - will not show the pressure she was put under by the Policia Judiciaria.

Lawyers will also fear that the interviews with Mr and Mrs McCann were so arduous, police will try to use them to show discrepancies in their stories.

Portuguese police have already leaked allegations to the local media that the accounts of the night given by the Tapas Nine do not add up.

A senior detective at Scotland Yard said: "The tape-recording of interviews is a fundamental principle of UK law now and ensures suspects' rights are kept in place. There can be no misinterpretation of what is said because of what is recorded. Translators make their own interpretations too."

The McCanns and their friends - who were dining together in a tapas bar on the night Madeleine went missing - face further interviews in the coming days. The head of the Policia Judiciaria has intimated that the friends will be quizzed in Britain by Leicestershire police but in the presence of Portuguese detectives.

It was claimed yesterday that the McCanns will also be interviewed next week after detectives from the Algarve arrive with an official request and 14 pre-prepared questions.

The McCanns deny any involvement in Madeleine's disappearance.