IF YOU GO down to the Square on Friday, you’re sure of a big surprise. Because, at 12.30pm precisely – and the precisely is very important – hundreds of people will suddenly lie down for five minutes.

Then they’ll get up again and melt away, as quietly as they came.

Why will they do this? Because they are taking part in a flash mob, a gathering of people in a public place who perform an unusual or seemingly pointless act for a brief time, before dispersing and going about their business.

Friday’s flash mob will, hopes organiser Lorna Trent, help publicise the start of BCHA’s Sleep Safe Campaign to increase donations and support for the town’s St Paul’s Homeless Shelter.

“By taking part people will help increase awareness of the harsh reality facing those that have nowhere safe to sleep,” she says.

Lorna is hoping that 500 supporters will come, maybe even some in their pyjamas – to represent the number of people helped by the St Paul’s Shelter each year.

“We want people to think about what it would be like to sleep on a street,” she says.

If your reaction to this is that it’s a load of nonsense, then think again. The power of the flashmob is everywhere, and is particularly loved by advertising agencies.

T-Mobile’s Life’s for Sharing dance, recorded at Liverpool Street Station, has been viewed on YouTube by a staggering 29 million people.

In Quebec the state used a flash mob to get across its message about putting litter in bins. Organisers placed a plastic bottle on a shopping mall concourse close to a litter bin.

As shoppers walked by, messages flashed up onto the screen about the millions of tonnes of plastic waste we chuck away each year.

Finally, after a few minutes, a lady shopper stoops to pick up the offending bottle and pops it in the bin... to rapturous applause from over 1,000 flash mobbers who had quietly positioned themselves in the mall. As the applause and cheering rings throughout the complex, the overwhelmed shopper starts bowing and waving.

Perhaps the greatest flash mob hit of all is the one perpetrated by Alphabet Photography of Philadelphia last November, when their Christmas mall flash mob astonished shoppers by standing up, one by one, to sing the Hallelujah Chorus. More than 33 million delighted viewers have seen this.

As a concept, flash mobbing is relatively new although the first event, created by senior editor at Harper’s magazine, Bill Wasik, didn’t go quite to plan.

His concept to playfully target a New York retail store went wrong when they were tipped off prior to the event but things improved with the flash mob he organised at Macy’s in June 2003, when 100 people turned up to buy a rug.

Even Bournemouth has not been immune, we’ve had singalong flash mobs in the lower gardens, a silent disco, and in December last year, a flash mob dance at the foot of Richmond Hill.

But why do we like doing this?

According to Lorna Trent we enjoy doing something different. “It’s not angry, it’s a happy way to publicise something.”

And 33 million people can’t be wrong.