The guitarist plans to write an autobiography

The film, to be broadcast on Tuesday, shows an emotional Townshend being quizzed at Twickenham police station.

A BBC crew filmed the Child Protection Team for 18 months to make the series.

Footage shows "a living legend reduced to being asked if he has learning difficulties", producer Bob Long told The Independent. "It's a big leveller."

Cautionary tale

Townshend's police interview dominates the first of a three-part series entitled Police Protecting Children.

"In a way I wish we hadn't filmed Townshend, because he takes away from the real pornographers," said Long, whose team was on hand to record the arrest.

"But he serves as a cautionary tale - don't be tempted to look at child porn because you life might be ruined," Long told The Independent on Sunday.

"His lawyers would have given anything for the documentary not to happen. But they took no legal action, I think because they would have lost."

Townshend, 58, was arrested after a child pornography website in Texas was infiltrated by the FBI, who passed on details of 6,000 Britons who had used their credit cards to access images.

His lawyers would have given anything for the documentary not to happen Bob Long

The guitarist admitted looking at the website, but said it was for research purposes. E-mails to child protection charities supported his claims.

Townshend was released with a caution and placed on the sex offenders register.

On Monday he returns to the UK stage with one of three London gigs, before playing a one-off performance of rock opera Tommy next month in aid of a children's cancer charity.