Iran is privately being blamed for a major cyber-attack on the BBC earlier this month that blocked access to its popular Persian TV service and disrupted the Corporation’s IT.

The multi-pronged 2 March attack took down much of the BBC’s email, overloaded its telephone switchboard with automatic phone calls, and blocked a satellite feed for the BBC Persian station. BBC servers were also on the receiving end of a DDoS attack.

In an unprecedented tactic, the BBC has trailed a speech to be given this week to the Royal Television Society in which Director General Mark Thompson will mention the attacks in some detail while stopping short of formally naming Iran as the perpetrator.

"It now looks as if those who seek to disrupt or block BBC Persian may be widening their tactics," Thompson will reportedly say.

"It is difficult, and may prove impossible, to confirm the source of these attacks, though attempted jamming of BBC services into Iran is nothing new and we regard the coincidence of these different attacks as self-evidently suspicious. We are taking every step we can, as we always do, to ensure that this vital service continues to reach the people who need it.”

Iran’s motivation for the attack - and few seriously doubt that Iran is the most likely culprit - is believed to be viewing figures released by the BBC only days before the attack showing the rising popularity of its Persian TV channel, which has doubled its audience to 6 million people.

Iran has previously tried to jam the radio signals for service, which marks the 2 March attack out as a significant escalation.

The country heavily moderates and controls access to the Internet or its own people, including slowing connection speeds to disrupt the distribution of video by its citizens to foreigners.