In an assessment of the security threat facing the UK, MI5 Director-General Jonathan Evans predicts a successful and memorable London Olympics but expresses growing concern about Iran.

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The head of MI5 says the Olympics Games is not an easy target for terrorists, writes Channel 4 News Home Affairs Correspondent Simon Israel.

Jonathan Evans told an invited audience in the City last night that while there's no such thing as guaranteed security he predicted a successful and memorable games.

The director general used his first public speech in nearly two years to deliver an updated broad assessment of the terror threat to the UK and its citizens.

But again there are no numbers - no quantifying of the threat, no details on the plethora of networks plotting some attack or other.

The Olympic Games, he says, have dominated much of the thinking but added: "..the Games are not an easy target, and the fact that we have disrupted multiple terrorst plots here and abroad in recent years demonstrates that the UK as a whole is not an easy target."

'Threat intelligence'

Inside venues are considered the most diffcult given the security arrangements, but an attack anywhere would be seen as an attack on the Olympics.

The security services have been planning for the worst, another 7/7 or a Mumbai-style attack - even another 9/11 (hence the proposal to place surface-to-air missiles on top of tower blocks).

They haven't stopped trying, but we have got better at stopping them. Jonathan Evans

But that is not what they are currently predicting. There are suggestions there's been a significant increase in "threat intelligence" but little of it amounts to credible plots.

In Monday night's speech the head of MI5 said "in back rooms and in cars on the streets of this country there is no shortage of individuals talking about wanting to mount terrorist attacks here".

The security think-tank Royal United Services Institute (RUSI) has indentified 43 potential plots or serious incidents since 9/11.

MI5's assessment is there's been 11 credible terror plots is that since then, which amounts to one a year.

Mr Evans said disruption and supression is leading to a form of stalemate - "They haven't stopped trying, but we have got better at stopping them."

Concern about Iran

Channel 4 News understands that close to 600,000 people will have gone through accreditation process by the time the games get underway and out of that only a a tiny number have come up on MI5's radar.

Security sources refused to say if some of the "hits" were individuals assigned to visiting international teams.

A return to state-sponsored terrorism by Iran or its associates, such as Hezbollah, cannot be ruled out. Jonathan Evans

The head of MI5 also expressed growing concern about Iran.

It's been revealed that MI5 has in the last year has significantly reinforced a dedicated unit, fearing that crunchtime may arrive next year over Iran's nuclear intentions. and the UK is widely seen as a potential target given recent attempted terrorists plots against Israeli interests.

He warned: "A return to state-sponsored terrorism by Iran or its associates, such as Hezbollah, cannot be ruled out as pressure on the Iranian leadership increases."

He also described the extent of cyber espionage and cyber crime as astonishing - on an industrial scale, and MI5 was currently investigating attacks on more than a dozen companies.

One un-named example he gave was a major London listed company which lost £800m, not just through intellectual property loss but also from commercial disadvantage in contractual negotiations.