Colin Sutton, a former senior investigating officer with the Metropolitan Police, said there is still a possibility the sniffer dogs being used by British officers at wasteland in Praia da Luz can find something new in the investigation into Madeleine McCann's 2007 disappearance.
He spoke to ITV News Correspondent Martin Geissler in Praia da Luz.
Police have shifted their investigation from the centre of the town where Madeleine McCann went missing to an area of scrubland a mile away.
Madeleine McCann search police are focusing on an area where ground-penetrating radar equipment has picked up an image beneath the soil.
Seven years on from Madeleine McCann's disappearance, British detectives are in Portugal to meet with police.