The 57-year-old musician, who said he had done so "purely to see what was there", issued a frank admission on Saturday confirming he had used his credit card on one occasion to access a site, but was not a paedophile.
Campaigners yesterday condemned his actions as "wrong-headed and illegal" and described his explanation as no excuse.
Mark Stephens, a lawyer with Finers Stephens Innocent who founded the Internet Watch Foundation, said: "It is misguided and illegal to look at or download paedophilic material and if you do, you are likely to go to prison."
The statement by the Who star idolised by fans since the 1960s said: "I am not a paedophile. I have never entered chat rooms on the internet to converse with children. I have, to the contrary, been shocked, angry and vocal (especially on my website) about the explosion of advertised paedophilic images on the internet."
Townshend's statement went on: "I have been writing my childhood autobiography for the past seven years. I believe I was sexually abused between the age of five and six-and-a-half in the care of my maternal grandmother, who was mentally ill at the time.
"I cannot remember clearly what happened, but my creative work tends to throw up nasty shadows particularly in Tommy (the Who's rock opera)."
But Mr Stephens rejected his explanation and added: "If he was abused as a child, one feels sorry for him but it doesn't present anyone with an excuse for doing something illegal."
Townshend's statement concluded: "On one occasion I used a credit card to enter a site advertising child porn. I did this purely to see what was there. I spoke informally to a friend who was a lawyer and reported what I'd seen."