The broadcasting watchdog Ofcom agreed to investigate after Teachers’ TV producers warned there was a risk that pupils whose school was being featured on the channel might stumble on to adult channels.

Teachers’ TV, which receives pound;20 million per year from the Department for Education and Skills, will be one year old next week.

An independent study on the channel showed it has some 280,000 viewers a month and that eight out of 10 teachers who watch it say it has improved their work.

Next month, Sky plans to reclassify Teachers’ TV as a specialist rather than a documentary channel. It is about the 180th channel viewers might now reach on Sky, close to the National Geographic and UKTV History channels.

Changes could put it between 250th and 300th, among channels including Dating TV, GayDate TV and the pornographic Red Hot and Television X.

Nigel Dacre, chief executive of Teachers’ TV, said: “We think it is, quite frankly, disturbing that an education and teaching channel is going to be put between dating channels and adult channels.

“There is a problem for parents and children who will be flicking through those channels to find a programme with their school in it.”

The fact that Teachers’ TV is broadcast on digital and satellite and only appears on Freeview in the early hours of the morning has made it difficult to improve its viewing figures.

But 90 per cent of teachers have now heard of it, and more than a quarter of those with satellite or cable television have tuned in for at least five minutes.

The channel’s original series can be downloaded free from its website. A tenth of its programmes are now watched this way.

Mr Dacre said: “For continuing professional development, it’s revolutionary. It’s reality TV for a good purpose.”

* michael.shaw@tes.co.uk

www.teachers.tv