The watchdog's chairman Lady Howe is expected to condemn the channel's use of sexually explicit material for its own sake on free-to-air television in a statement on Thursday.

She will add such material should only be shown on subscription channels, with explicit scenes on mainstream services restricted to documentaries and drama "within a dramatic or informative context".

The Commission will uphold complaints against the series Hot Lines and Compromising Situations. But while it can adjudicate on complaints against all broadcasters, it is powerless to take action against the channel.

A spokesman said: "Recent research by the BSC shows people are less concerned about sex on television if it is justified within a dramatic or informative context."

No power to ban shows

The Independent Television Commission can fine errant broadcasters

He added the research had shown people expected different standards from free-to-air television - which they felt went "straight into their homes" - than they did from cable and satellite channels.

But while the watchdog can bark - it cannot bite. The BSC has no power to ban such broadcasts or impose any other sanctions over broadcasters.

In Channel 5's case, that job falls to the Independent Television Commission.

A Channel 5 spokesman called the expected ruling "extraordinary", adding it was in step with guidelines laid down by the ITC.

He said: "We have to take notice of this, but they do not have the power to ban this. It is for the ITC and they have not got any problem with our late night schedule.

"What the BSC says seems to be clashing with the view of the ITC."

Overlap between regulators

BBC Television Centre: The corporation deals with its own taste and deceny matters

The ITC's chairman, Sir Robin Biggam, has urged the government to reduce the overlap between Britain's media regulators.

The government is currently looking at how to reform broadcasting regulation with the introduction of digital TV.

The BBC looks after its own fairness, taste and decency issues across all its radio and TV services, while the ITC regulates ITV, Channel 4, Channel 5 and satellite and cable channels. The Radio Authority does the same job for Britain's 200-plus commercial radio stations.

While the BSC can consider the same complaints about all these services, it cannot take the same action as the BBC, ITC or the Radio Authority.

Sir Robin told the Royal Television Society last week: "The current system of a tightly-regulated commercial sector and a self-regulated BBC needs a critical review.

"It is certainly difficult to see the markedly different systems surviving into the digital era when there will be much greater pressure on all free-to-air broadcasters as they fight to hold share of a reducing market.