Footballer Ronaldo made a public appeal on television

 British child abduction experts were flown to Portugal last night in an "unprecedented move" designed to shore up the floundering police investigation into the abduction of Madeleine McCann. 

The development came as Cristiano Ronaldo, the Portugal and Manchester United footballer, made a public appeal for help to find the missing three-year-old.

Claims that a British paedophile network could be responsible for her kidnapping strengthened yesterday, but criticism of the police inquiry continued to mount.

The two specialist ''profilers'' from the Child Exploitation and Online Protection Centre will advise the Portuguese police on the behavioural traits of paedophiles

It also emerged yesterday that calls from all across the UK are being passed on to Portuguese authorities through police in Leicester. Fleeting hopes of an end to the ordeal of Madeleine's parents, Gerry and Kate, were dashed last night after reports of a sighting of her in north Portugal were dismissed by police as a false alarm. Ronaldo, who was recently voted Footballer of the Year, attempted to boost the search after volunteering to make a televised appeal.

He said: "I was very upset to hear about the disappearance of Madeleine and I would ask for anybody with any information to come forward. Please come forward."

Portuguese detectives claimed yesterday that they have 350 suspicious sightings and leads which are being followed, and officers have held formal interviews with more than 100 people.

Sources close to the investigation said a key line of inquiry is that Madeleine was "kidnapped to order" by a paedophile ring.

A list of British sex offenders with links to Portugal and particularly the Algarve has sent to police. A witness claimed to have seen a suspect stalking the area a week before the abduction and making a series of telephones calls. Madeleine, who is four on Saturday, was abducted from the family's holiday apartment in Praia da Luz, Algarve, on Thursday night as she slept.

At 5pm yesterday police set up roadblocks around the town of Nelas, 300 miles north of Praia da Luz.

There were reports of a blonde girl, apparently matching Madeleine's description, seen in a supermarket with a man she seemed reluctant to be with.

Television reports claimed that CCTV footage of the pair at the supermarket was being prepared to be sent to the McCanns for identification.

However, police discounted the sighting as a false alarm after the man was stopped in his car and confirmed as being the girl's father.

Chief Insp Olegario Souza, one of the police chiefs leading the investigation, said: "It was a false alarm. It is just one more follow up."

Following complaints about the Portuguese police inquiry, the British ambassador to Lisbon spoke out yesterday to defend the handling of the investigation.

After visiting Madeleine's distraught parents Gerry and Kate, John Buck emerged to say that the couple appreciated the Portuguese efforts and said specialists from the two countries were working well together.

He also revealed he had been in touch with Portuguese cabinet ministers and the office of the Prime Minister.

Mr Buck, who has visited the couple repeatedly throughout their ordeal, said after his latest visit: "I wanted to assure myself personally that the necessary links between British and Portuguese experts here on the ground were working well, and they are."

He added: "They (the McCanns) are very pleased with the collaboration of the British authorities, they are in close touch with Interpol and Europol and I know Kate and Gerry, with whom I have just been speaking over the last hour, are very grateful for their efforts."