Q&A: Terrorist threat

The head of MI5 Eliza Manningham-Buller has been speaking to police in London about the nature of the terrorist threat facing Britain. BBC security correspondent Frank Gardner was at the lecture.

How serious is the threat of terrorist attacks?

The threat is just as serious if not more so than it was at the time of the 11 September attacks on New York and Washington.

The Heathrow security alert earlier this year was not a political gimmick designed to make us back an attack on Iraq, she said - it was real.

The key message he took from the lecture was that - whatever people might think of the Iraq weapons debacle - the risk to Britain from terrorist groups linked to al-Qaeda was not imagined or exaggerated, but real and here to stay.

Who is most vulnerable to attacks?

British business is on the frontline. Ms Manningham-Buller wants the security advice to British infrastructure - fuel, power, water - to be extended to the food and chemical industries.

What are British security bodies doing to counter the threat?

It is a long hard slog. Within MI5, the Joint Terrorist Analysis Centre (JTAG) is processing about 100 pieces of intelligence a week that deal with potential plots.

They have managed to infiltrate some of the groups that are linked with al-Qaeda.

How long will it take to overcome the threat?

Ms Manningham-Buller fight against Islamic terrorists would be a long haul lasting for many years.

She said al-Qaeda remained sophisticated and resilient.