The couple were informed of the potential development while in
Germany, where they were appealing for information about their
four-year-old child. It is 35 days since Madeleine was abducted from
her bed in the Algarve resort of Praia da Luz.

The "credible"
call was taken from a man who wanted to speak directly to the McCanns,
according to a Spanish police source. It was traced to an unregistered
pay-as-you-go phone from an unidentified country but not thought to be
Morocco, where a previous possible sighting of Madeleine was reported.

The
caller did not reveal his identity or nationality, but the information
was considered important enough to alert Mr and Mrs McCann, the source
said.

At around 3pm on Wednesday, the couple - who were about to
go to Tempelhof airport in Berlin to fly on to the Netherlands - were
advised that the caller might try to contact them, so they stayed on at
the British embassy.

At 6pm, journalists travelling in the
eight-seater private jet with the McCanns were told by the flight crew
that there might be a change in destination. They revealed they had
been asked to draw up a new flight plan involving a possible change
from Amsterdam to East Midlands Airport.

It was thought the McCanns might need to go back to the UK to talk to advisers about the call.

But
all efforts to re-establish contact with the man failed and the couple
decided to go on to Amsterdam. They left Berlin at 7.30pm, three hours
later than planned, for the hour-long flight to Schiphol Airport in
Amsterdam to continue their search. Mr and Mrs McCann are thought to be
on standby, ready to return to the UK if necessary.

A Spanish
police source said: "A man called saying he knew where Madeleine was
and wanted to speak to the McCanns. This did not appear to be a crank
call and the information was felt credible enough to warrant the couple
being informed immediately."