Through the Foreign Office, Mr Brown arranged a meeting between senior Portuguese officers and the couple, which led to the release of details of a potential sighting of Madeleine being carried by her abductor on the night she went missing.

The Prime Minister-in-waiting's involvement emerged as Prince Charles and the Duchess of Cornwall also showed their support for the McCanns.

Gerry and Kate McCann heading to the local church in Praia Da Luz, Portugal, today

The couple may visit Rome this week to meet the Pope

They issued a statement which said they had been following the case "with deep concern for the parents and fervently hope that Madeleine will be safely returned to her family as soon as possible. Their Royal Highnesses' thoughts and prayers remain with Mr and Dr McCann at this very difficult time."

It was revealed that the McCanns may visit Rome this week to meet the Pope. The couple say their Catholic faith has sustained them since four-year-old Madeleine was snatched.

The Chancellor, who has a son a few months younger than Madeleine, spoke to Mr McCann on three occasions early last week and pledged support from the very top of Government.

A spokesman for the McCanns said: "The conversations took place against the background of the Chancellor's earlier offer to help when he met and spoke to other members of the family in the UK."

Brave face: The McCanns with twins Amelia and Sean

The McCanns said their meeting with police was "amicable and very constructive". They welcomed the decision to release details of a man seen in Praia da Luz on the night of Madeleine's disappearance.

He was said to be white, 35 to 40, medium build, 5ft 10in, wearing a dark jacket and light beige trousers. He was possibly carrying a child.

The McCanns said: "The release of this important information followed an earlier meeting we had with senior police officers. We feel sure this sighting of a man with what appeared to be a child in his arms is both significant and relevant to Madeleine's abduction."

The Chancellor was told by Gerry McCann that he was concerned police were not being 'forthcoming' with information

Portuguese police have known of the sighting for three weeks but because of laws which forbid the release of details of an investigation, it could not be disclosed.

In other countries, such a vital piece of the jigsaw would have been released early on in the hope of witnesses coming forward.

Although they have praised the efforts to find their daughter, the McCanns were said to be increasingly frustrated at delays and communication problems. The family threatened legal action to push for the information to be released.

Earlier the couple told how they are so haunted by the abduction of their daughter that they sleep with their two other children, two-year-old twins Amelie and Sean.

Kate, 38, said: "The twins sleep in the bed with us now. They help us to get through this. We are a strong family and they were so close to Madeleine, only 20 months apart."

In their first newspaper interview, the pair described how their lives have been turned inside out.

Gerry, also 38, said he has woken every day distraught at not receiving a call to tell him Madeleine has been found safe. "My waking thought is that the phone by the bedside has not rung and that means Madeleine has not been found."

Telling how she copes with not having her daughter around, Kate added: "I am better in the morning, it seems like a fresh start. Evenings are harder. I haven't been able to use the camera since I took that last photograph of Madeleine."

The couple spoke before taking Amelie and Sean to a playground where the two children played on the swings and slide and darted in and out of a Wendy house.

"The twins are so young they just get on with things but obviously we don't want them to forget about Madeleine,' said Kate.

"We are hoping to see a child psychologist next week to explain what has happened to Madeleine to the twins."

Kate also relived the moment she realised her child had been abducted. "For a few seconds there was total disbelief. It was terrifying. You just don't expect in a million years that this could happen."

Gerry added: "The way the scene was left means there was absolutely no doubt she had been abducted."