'Big Brother' faces up to the reality of TV ratings - its viewers have switched off

Viewing figures for the reality television show, which finishes tonight, have dropped and commentators have warned that the channel is in danger of relying too heavily on a tired format.

The sixth series has plumbed new depths, the 20-year-old Kinga Karolczak's actions following other scenes such as sexual fumblings in the hot tub between two contestants and plenty of groping between others. All have been seen as increasingly desperate measures to gain the viewers' attention.

Yesterday the show's makers, Endemol, were on the defensive again after claims that another female contestant, the self-confident Zimbabwean nurse Makosi Musambasi, was a jobbing actress. They denied the story.

Channel 4 has committed itself to at least two more series of Big Brother after its current contract with Endemol runs out at the end of 2005, with the option for a further two years after that.

The current series has averaged an audience of 4.4 million, a 22 per cent share of viewers.

While the series' average will be boosted by tonight's final - and with anything over the four million mark being eminently respectable for Channel 4 - this unofficial average is lower than the consolidated viewing figures for any previous series. Even the fourth Big Brother, dismissed as the dullest yet, was watched by an average of 4.6 million, while last year the show enjoyed a renaissance with average viewing figures of five million, a 25 per cent audience share. Channel 4 has played down the significance of Big Brother, maintaining that while it is an important part of its commercial success, generating funds for less-watched drama and current affairs, it is only a small element of its overall offering.

But it has not addressed, in public at least, the issue of what will happen when audiences lose interest in a bunch of youthful extroverts engaging in ever-more lewd antics in a quest for instant fame, causing the lucrative telephone voting to dwindle.

It is not just the contestants who have resorted to gimmicks to sex-up the series - the producers have also been up to some tired tricks. "Surprise" evictions are now a regular occurrence, while a sequence in which one of the housemates, Eugene Sully, was faced with the no-brainer decision of whether to take half of the prize money (no one told him that if he had resisted, the pot would have doubled) looked distinctly lacklustre. David Elstein, former channel Five chief executive, said Channel 4 had invested too much in the show to relinquish it soon. "Channel 4 is certainly heavily dependent on Big Brother," Mr Elstein said. "[The digital channel] E4 is hugely dependent on spin-off programming - it probably gets about a third of its revenue from Big Brother. I don't think we'll see Channel 4 giving it up any time soon. The risk you run is that it may burn out on you."

Conor Dignam, editor of Broadcast magazine, agrees that Big Brother is a banker for the channel, but warns this is unsustainable in the long term. "They will only have come to rely on it too heavily the year that it finally fails to deliver," Mr Dignam said. "While it still brings in the viewers, they're not going to reduce it. It's a bit like saying ITV relies on Coronation Street too much. There will come a year when finally the wheels come off Big Brother, when viewers become tired of it, or they miscast it."

The current series did not enjoy the same marketing push in its first week as in 2004, when the opening show coincided with the farewell episode of Friends.

Just before the launch of this series of Big Brother, Channel 4's chief executive Andy Duncan admitted the show had done the broadcaster few favours with politicians. "A lot of politicians don't watch telly and if they do, they tend to watch the news. The sense that Channel 4 was doing Big Brother and not much else was a bit of a lazy perception. Among its audience it's absolutely loved, but it's one of the most polarising things we do," Mr Duncan said.

Who's watching the programme?

* BB1: 4.7m/26 per cent share

* BB2: 4.6m/24 per cent share

* BB3: 5.8m/28 per cent share

* BB4: 4.6m/22 per cent share

* BB5: 5.0m/25 per cent share

* BB6: 4.4m/22 per cent share (not consolidated, does not include tonight's final)