Guardian newspaper editor Alan Rusbridger said the decision to detain David Miranda "seems to me a clear misuse of a law."
Speaking at the Edinburgh International Book Festival, he called for a wider public debate about mass surveillance, praised the value of the information leaked by whistleblower Edward Snowden and described US soldier Bradley Manning's 35-year sentence "staggering".
Mr Rusbridger said the "strong suspicion" has to be that the detention of Mr Miranda at Heathrow Airport was "quite a carefully planned operation and wasn't random".
"There has to be a debate. There hasn't been much of a debate in this country yet because everyone is a bit complacent about it," he said. "In the end it's for people to decide."