Gerry and Kate McCann with their twins in Praia Da Luz yesterday

The parents of Madeleine McCann said they were clinging on to the hope that the four-year-old is safe and being looked after by someone who wanted a daughter of their own.

Speaking today from Madrid, where they have flown to highlight the plight of their missing daughter, Kate and Gerry McCann said they believed that she was still alive because they have no evidence to suggest otherwise.

Mr McCann said: "We also pray that the person who has her gives her up voluntarily and drops her at a church or a safe place". It is now 29 days since Madeleine was taken from her bed in the Algarve resort of Praia da Luz.

As the McCanns prepared to launch their European search, the police investigation into the disappearance of Madeleine looked increasingly desperate last night as detectives revealed they were following tip-offs from clairvoyants.

Intensive searches and a highly scrutinised police inquiry have failed to secure a breakthrough in the search for the girl four weeks after she was abducted.

Police faced further ridicule last night as it was revealed they were trawling through hundreds of reports from British and Portuguese psychics claiming to know the whereabouts of Madeleine. One alleged vision had led them to search in Seville in Spain.

The Judicial Police, who are leading the inquiry, said they had two dossiers, 3ins thick, of apparent visions of the little girl, and are following them up on the basis that one could be from the abductor.

Police spokesman Olegario Sousa said: "We can't put these messages in the bin. We must check them all in case it might be from the kidnapper."

Mr Sousa said some descriptions were as vague as dreams about a man in a house with trees and a road. But he said that others include precise locations or co-ordinates, which they will follow up.

"Just a few days ago we got one address near Lagos but it didn't amount to anything," he said. He added that it was only one line of investigation.

In another surprising move, Portuguese police last week instructed their counterparts in Britain to raid an address in south London in the belief that Madeleine may have been inside.

Debbie Seepersad's property in south Norwood was searched but nothing was found.

She said she had never been to Portugal and had no connections to Madeleine. She said: "I really thought it was a wind-up."

Criticism has mounted against the police investigation, which local media say has "stalled".

Mark Williams-Thomas, a former detective who worked on the Sarah Payne murder inquiry and other paedophile investigations, said: "You have to say that they made serious errors. They did not do the basics. A major window of opportunity was lost."

After accusations of initial tardiness, Portuguese police have thrown all their resources into finding Madeleine. Up to 1,100 officers were working on the case at one stage.

Robert Murat remains a formal suspect and others are still being investigated. His friend Sergey Malinka has been assisting police but is not a suspect.

Mr Sousa said: "We are not sitting here with our arms crossed doing nothing."

Mr and Mrs McCann are expected to meet police chiefs again in the next few days for an update on the case.

Asked whether he was privy to any information from police which gave him extra hope, Mr McCann said: "We may have little bits of extra information. There are points we have. The investigation is as good as it is ever going to get. It has been four weeks now and it has evolved. We are hopeful.

"When Madeleine went missing it started off with us thinking in terms of minutes until we found her. Then minutes became hours, days and now weeks."

Mr McCann said although Madeleine's abduction was a parent's worst nightmare, they had found comfort from their two other children, two-year-old twins Sean and Amelie, who are being looked after by relatives in Portugal while the McCanns make their trips around Europe.

Early next week the pair will continue their mission to find Madeleine with a trip to Berlin and Amsterdam.