"It's opening up that whole debate," added Harry Ferguson, who worked for MI6 overseas in the 1980s and 1990s. More safeguards were now needed to protect the private citizen, he told AFP.

He said the show accurately reflects the rapid changes in the world's second oldest profession in the last 20 years but also how the relative ease of electronic intelligence gathering has created its own problems.

The 9-11 Commission in the United States highlighted deficiencies in piecing together intelligence before the September 11, 2001 attacks.

And after the US-led invasion of Iraq in March 2003, claims that president Saddam Hussein was amassing weapons of mass destruction were later disproved.

Ferguson, who has written two books based on his time with a customs team targeting heroin smugglers, said choosing the right information was getting harder as technology threw up more and more potential leads.

It was also forcing some terrorist suspects to go back to "Cold War" espionage tactics like "dead-letter drops" and "brush contacts", knowing they cannot escape the spies electronically, he added.

"The buzzword 'is data-mining'. Now there's so much gathering of intelligence but finding out where the important information is is where a lot of energy is being spent," he said.

"(The intelligence services) are always complaining they haven't got enough manpower to do it.

"What really needs to happen when it comes down to it is hard surveillance, people on the ground, talking to contacts."

Ferguson, who also hopes the show would encourage children to be the spies of the future, said that appeared to be the case after two men arrested under anti-terror laws last week were released without charge Wednesday.

Angry Muslim leaders in Birmingham, east central England, have said there was no evidence to arrest or charge the pair - or seven others also detained - despite a six-month surveillance operation.

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