Commission spokesman Andrew Ketteringham

The commission has re-written its code on taste and decency because it believes some current warnings are not straightforward enough.

Its chairwoman, Lady Howe, said: "The code provides authoritative guidance on what is and what is not acceptable for the broadcast portrayal of sex, violence and other matters of taste and decency.

Broadcasters must make warnings clearer, says watchdog.

"It is backed by the commission's own audience research, which suggests that these sensitive issues continue to be important, and by the commission's experience in handling complaints from viewers and listeners."

Communications Director, Andrew Ketteringham, said people wanted "very clear" warnings.

"They are telling us they would prefer the broadcasters to say 'This programme contains strong language'.

"We hear announcers make all sorts of announcements prior to some programmes but what is certainly the case sometimes is it is not quite as straightforward as the general public would like," he said.

The code points out that programmes can cause particular offence when viewers or listeners are shocked or alarmed without any warning.

Parents are concerned about the effect of sudden violent or sex scenes on their children, said Mr Ketteringham, which lends support to the concept of "labels".

He added: "This is one of the reasons why the watershed is such an important principle. There is a good deal of suport for it.