MI5 set for biggest security operation for 60 years

The initial security budget of £600m has risen to £1bn (EPA)

MI5 is carrying out its biggest operation since the Second World War, with almost all of its 3,800 staff mobilised for the London Olympics which will take place amid rising concerns over the possibility of terrorist attacks.

Although there is said to be "chatter" among jihadist groups about the Olympics, security officials have refused to discuss if any cogent plots have been discovered. Senior sources say that at the last major sporting event seen as a target, the Commonwealth Games in India, planning by terrorist groups began around three months before the event started.

i understands that the Security Service has installed a new monitoring and intelligence gathering system to ensure the safety of the Games. This includes security checks on more than 540,000 people, monitoring militant groups and also liaising with foreign intelligence services.

The new system developed by MI5 for the Olympics, including computerisation, details of which are classified, has been in place since last October. It is deemed to have been highly successful, and will be kept in use after the Games have finished.

While MI5 says it does not need extra government funding for its Olympic security operations, with the figure needed having been included in its previous funding round, the costs to the public have risen from the original estimate of £600m to £1bn.

One of the reasons for this was that Locog underestimated the number of staff needed for the 34 Olympics venues. The original figure of 10,000 has now been raised to 20,000.

MI5's role would be to specifically focus on those who pose a terrorist threat to the event.

Annual leave will be cancelled or restricted at the agency and agents who would have been involved in counter-espionage have been moved to terrorism duties.

In addition, about 13,500 military personnel, 4,000 more than are currently serving in Afghanistan, will be deployed on the security operation.