Thomas Drake is a former senior official at the highly-secretive National Security Agency.

He was accused of passing on information to a journalist about a government computer programme he considered wasteful.

After the government's case against him fell through, he pleaded guilty to a minor charge of overstepping his authorisation when using a government computer and was sentenced to one year's probation.

Mr Drake said that following the 9/11 attacks, laws passed against the electronic surveillance of US citizens without a warrant, except under certain circumstances, were bypassed.

"Not only did the wheels came off, we were in an entirely different vehicle," he said. He added that "aspects of a secret surveillance state have begun to manifest" in the US.

You can watch the full interview on BBC World News on Wednesday 8 May at 14:30 and 20:30 GMT and on the BBC News Channel on Thursday 9 May at 00:30 BST.

Watch more clips at HARDtalk's website.