They have become convinced the four-year-old will not be found alive.

Officers in Leicestershire have come to share the view of the Portuguese police after sniffer dogs detected 'the scent of death' in the Algarve holiday apartment from which she vanished.

The two springer spaniels, said to be capable of detecting blood and human remains, were used in the investigation in August.

One picked up a 'scent of death' on items ranging from mother Kate McCann's clothes to Madeleine's favourite soft toy Cuddle Cat.

This evidence, and the alleged discovery of specks of blood in the McCanns' Ocean Club apartment in Praia da Luz, convinced the Policia Judiciaria - Portugal's criminal investigation department - that Madeleine, from Rothley, Leicestershire, died there on 3 May.

It is now thought that officers in Leicestershire have also come round to believing the same theory.

Pain: Kate and Gerry McCann still believe Madeleine can be found alive

A legal source close to the Portuguese police said that evidence gathered by officers in Britain led to Gerry and Kate McCann being named as suspects.

He added that the inquiry, which initially focused on Madeleine being abducted, changed direction after Leicestershire police offered to help by taking sniffer dogs to the apartment.

"The British police came up with the evidence the Portuguese needed to make the McCanns suspects in Madeleine's disappearance," said the source.

"It was the British police's idea to have sniffer dogs search the apartment. That day marked the turn in the case."

A month later, on 7 September, the McCanns, both doctors, were declared official suspects. The source said: "If it wasn't for the involvement of the British police, the McCanns probably would not have been made suspects.

"The Portuguese police had their suspicions two weeks after Madeleine disappeared due to the discrepancies between witness statements.

"The friends, the McCanns and the employees at the Ocean Club had stories that just didn't match up.

"At that stage they couldn't do much with their suspicions. It was only when the British got involved that the inquiry began to move on quite quickly."

Carlos Anjos, president of the Judicial Police Inspectors Union, said Portuguese detectives have an 'excellent' working relationship with British police without 'a single misunderstanding'.

He added that despite all the resources at the McCanns' disposal, their campaign had so far produced 'nothing', as opposed to that of the police who have obtained the only credible evidence.

�?A former South African detective with a record of finding missing children was called in by Kate and Gerry McCann.

Danie Krugel pinpointed an area in Praia da Luz where he believed Madeleine had - at least - passed through.

He spent four days searching in July after they were bombarded with emails saying he should be called in.

Mr Krugel said: "I went there to find her alive and according to my test results she was in the area of Praia da Luz. She was not in Spain or Morocco."

As a result of his work, Portuguese police called in British officers to help, a source close to the McCanns said.