FOR devout Catholics Kate and Gerry McCann, the midweek meeting in Rome with Pope Benedict XVI was an occasion from which to draw strength.

For the media, the sight of the Pontiff blessing a photograph of their missing daughter Madeleine allowed the story to run prominently on television and in print.

Today in Glasgow, there will be another photocall as 400 balloons carrying an appeal for the four-year-old are released at Bankhead Primary School in Glasgow where Madeleine's aunt, Diane McCann, is a teacher. Campaigners hope the balloons, carrying tags with the phone numbers of the family, will even drift across Europe.

Diane McCann said: "The family is delighted with the efforts of my colleagues and the pupils at the school - any help that can keep Madeleine in the public eye is very gratefully received."

But, just over four weeks after her disappearance from the Portuguese resort of Praia da Luz, some PR experts fear that keeping Madeleine in the public consciousness will prove increasingly difficult.

Phil Hall, a former News of the World editor, said he believed the tide of publicity would ebb following the Papal meeting.

He said: "I think it is coming to an end this weekend; I don't see how much more they can create to keep it on the front pages and I do think, however much the British public care about this situation, interest is starting to wane - we've just seen it all.

"Some journalists have been there [Portugal] for a month now and it is wearing thin.

"It is one thing doing that if you get front-page news out of it; it is another when you get picture captions."

So far, "Team McCann", buoyed by an enormous wave of public sympathy, has achieved near-blanket coverage of their plight. The family has received advice from UK public-relations company Bell Pottinger and a succession of photos and video clips have fed a media pack hungry to fill news bulletins and front pages.

However, they will be aware that the public, however sympathetic, will lose interest if no significant details emerge.

News organisations are likely to begin withdrawing from Portugal soon, leaving coverage of the story to local freelances and news-wire staff.

The unfortunate reality for the McCanns is that the majority of missing-children cases do not require prolonged campaigns. Research from the United States' Department of Justice published in 2002 suggests that, in 90 per cent of cases where a child is taken by a stranger, they are found within hours.

In the US experience, 40 per cent of children taken by strangers are killed and a further 4 per cent never found. In cases where the child is missing for months, FBI investigators are hardened to the likelihood that in many cases they will find the child dead or not find them at all.

American organisations such as the National Centre for Missing and Exploited Children maintain that children can still be found alive months or even years after being taken. Some US campaigners also offer templates for campaigns that last for longer periods; six weeks, for example, with activities such as classic-car rallies and blues concerts scheduled at various points.

PR adviser Jonathan Haslam, who runs an agency specialising in crisis management, said it was inevitable that media attention would wane.

He said: "The McCanns have to think about how they keep a European media interested.

"The UK media have been fantastic in the way they've supported them, but they cover the UK. Maybe that's [not] necessarily the area they have to look at."

The couple appeared to be acting with that PR consideration in mind last night as they headed for Madrid at the start of a ten-day tour that will taken in Berlin, Amsterdam and even Morocco.

While in Madrid, they are set to meet Denise Holt, the British ambassador, before taking part in a television show dedicated to missing children.

It emerged yesterday that Portuguese police were trawling through hoards of e-mails and messages from clairvoyants who believe they know Madeleine's whereabouts.

Force spokesman Olegario Sousa said that the psychics' claims were being taken seriously.

He added: "If there are indications which are enough to follow then we will go."

Psychics have also contacted several news organisations in the UK about Madeleine.