BBC News 24 was relaunched in December

It follows reports that more than 55 days' worth of programmes last year were watched by so few viewers that they scored zero in official ratings.

The channel with the most zero-rated output was BBC News 24, which recorded 472 hours of "unwatched" programming, the Media Guardian website said.

But the BBC said it was continuing to "grow and perform strongly".

A BBC spokeswoman said the figures also failed to show that during the same period, Sky News had also had viewing figures of zero on a sample weekend from the survey at 0215, 0230, 0315, 0500 and 0515 GMT.

She said that at the same time News 24 was recording viewing figures as high as 17,000, and that few digital channels were broadcasting all through the night.

Freeview success

"Many channels are recording lower figures at the moment because this is the nature of viewing in the digital age," the spokeswoman added.

She also said the News 24 figures did not take into account the fact that the channel's coverage was being simulcast on BBC One at the same time.

More households were switching over to digital reception, thanks to the success of set-top boxes which can pick up Freeview channels.

More than 2.5 million were expected to have been sold before Christmas, and the spokeswoman said latest figures were expected to "easily" surpass that.