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But despite exchange trips to the African Big Brother house, multiple evictions and new housemates (and, cynics might even claim, phoney bomb scares), this season's show seems to have failed to capture the public imagination in a way that previous series have.

This has been reflected in a declining audience - Barb figures reveal that young audiences in particular are turning away from Big Brother and that Channel 4's digital channel, E4, is being hit particularly hard.

The show has become older and more female-oriented, which has implications for both agencies and Channel 4 itself.

Big Brother has become a mainstay of the Channel 4 schedule and plays a significant part in delivering its youth audiences. Its success in delivering these audiences is crucial to Channel 4 when it comes to deal negotiation and the worry is that the station will reap what it has sown this autumn.

Compared with Big Brother 3, late peak 16-to-34 adult audiences on Channel 4 are down 15 per cent. On E4, which has shown streamed coverage of events in the Big Brother house, audiences are down even more - for the same audience peak, Big Brother programmes are down 50 per cent.

While the Barb figures reveal that audiences are voting with their remote controls, anecdotal evidence also seems to suggest that Big Brother may have run its course.

A year ago, the newspapers were full of stories about the antics of Jade Goody, the porcine Big Brother contestant. One year on and it seems that the only consensus among the newspapers is that this year's Big Brother is boring.

Critics have identified the housemates as the problem - received wisdom is that this is because the programme makers chose people that are closely aligned to typical Big Brother viewers.

"Figures are down because there has not been any scandal," Paul Curtis, the managing director of Viacom Brand Solutions, says.

But Andy Zonfrillo, the broadcast director at MindShare, thinks that the problem may be deeper than this. "You can partly say it's the people but the fact is that reality TV is not innovative TV anymore, and it's no longer guaranteed to grow ratings," he says.

You might think that this is surely bad news for the programme's sponsor, O2, but Lawrence Munday, the managing director of Drum PHD, which negotiated the sponsorship deal, claims that the show still has value.

"We've been involved with Big Brother for three years and every year is different. The perception is that it isn't doing well but if you look at the figures, it is doing well in audience terms," Munday says.

However, he concedes that there has been a decline in young audiences, but claims that this might be down to the recent spell of clement weather.

Channel 4 say that Big Brother is still performing well, but has a hard act to follow compared with last year's series. A spokeswoman says that the 10 pm slot on Channel 4 averages 4.4 million viewers (a 22 per cent share) with Big Brother, compared with an average of two million (a 10 per cent share) when it is not being shown.

She also says that on E4, the series contributes to the digital channel taking a higher daily share than Sky One, UK Gold, BBC3 and ITV2 in multichannel homes.

Curtis says that the majority of the recent reality TV shows - including The Club, Reborn in the USA and Murder Game - have not been a hit with young audiences. However, he thinks that reality TV still has mileage.

"We think reality TV can still push the boundaries of voyeurism if the TV and the creative community are adept at redeveloping the format," he says.

Channel 4 remains committed to Big Brother, although perhaps revealingly there are to be no more celebrity specials.

Channel 4 is currently looking to recruit a new director of television after the forthcoming departure of Tim Gardam. It will be up to his successor (and all eyes are on five's director of programmes, Kevin Lygo) to see how much longer the show will run.