Investigators searching for Madeleine McCann must have access to previously unseen files held by Portuguese police, a spokesman for her parents said.

The files, which include thousands of pages of information passed to the police after the case was officially closed, are reported to have been seen by several British newspapers.

Family spokesman Clarence Mitchell said: "Kate and Gerry have made it clear that they were shocked to see the lack of follow-up work done by the Portuguese police since the investigation was shelved.

"All the information in these files must go to the private investigators as they are the only people still looking for Madeleine."

Madeleine was nearly four when she went missing from her family's holiday apartment in the Algarve village of Praia da Luz on May 3 2007 while her parents dined with friends nearby.

Despite a massive police operation and huge publicity worldwide, she has not been found.

Four months after she disappeared, Portuguese police made both Mr and Mrs McCann arguidos, or formal suspects, in the case.

Two days later, on September 9 2007, they returned to Britain with their two other children, twins Sean and Amelie.

In July 2008, the Portuguese attorney general shelved the investigation and lifted the arguido status of Mr and Mrs McCann.

The couple insist they will continue to believe Madeleine is still alive until presented with firm evidence to the contrary and have vowed to keep looking for her for as long as it takes.

The Daily Mail reported that among the leads included in the file was CCTV footage of a young girl said to look like Madeleine being led into a New Zealand supermarket by a man, seven months after her disappearance. One report mentions a British man called George who saw a small, distressed blonde girl being dragged along a road to Faro airport in Portugal on the night she went missing (see story below).

Another report mentions a young girl being held at gunpoint on a French motorway by a half-naked man in August 2008.