The Who rocker Pete Townshend has received a letter of support from a police officer who headed the investigation into his child porn offence.

The musician was targeted in 2003 after he used a credit card to access a website that advertised child pornography.

Townshend accepted a police caution after deciding not to fight the charge, although he insists he only surfed the site as part of research into the horrors of the child porn industry.

He has been talking about the experience as he promotes his new book, Who I Am, and has now revealed he recently received a note from one of the officers who worked on the case, declaring his innocence.

The rocker tells BBC Radio 4 show Front Row, "I accepted a caution from the police which led to me being labelled a sex offender but I did nothing wrong. What happened is that I did not enter the website, I did make the transaction which I immediately cancelled... There was no evidence except from the mea culpa (sic) of the credit card.

"So, I was charged, cautioned and put on the sex offenders' register as a signal. But I don't think it was quite right... I got a letter from a policeman three or four days ago who headed up the investigation who said, 'We knew that you weren't a paedophile, we knew that you weren't a child molester.'"