Analysts have warned that a mainland attack by dissident Republicans coupled with an uplift of terrorist activity in Northern Ireland remains a realistic prospect during the Olympics.

There are concerns that the flat-lining economy coupled with the growing enthusiasm of a new breed of terrorists is creating the right conditions for dissident groups to grow.

And security professionals believe that terrorists are looking to carry out an attack on the UK mainland at a time when the eyes of the world will be on the Olympics.

Justin Crump, CEO of risk management consultancy Sibylline, said that the emergence of three main groups – the Real IRA, the Continuity IRA and Olagh na Heireann – had now been joined by some 30 smaller contemporaries.

In addition, he pointed out that former members of the Provisional IRA with bomb making experience were still in circulation – and difficult economic conditions meant it was more likely that they could find their way back into terrorism.

Mr Crump said: "The wish of these groups would be to carry out a successful bomb attack in London – the time they are likely to have a go is during the Olympics.

"We have seen in Northern Ireland that they have some capability reasonable sized car bombs – the games will be a time when the world's media will be in London."

The terrorists had already pulled off a hoax in the Capital earlier in the year, when they used a recognised code word and caused disruption, said Mr Crump.

He predicted that the terrorists will have closely observed the response to the alert, adding: "We could potentially see a further hoax or a small device."

As well as dissident Republicans, Mr Crump highlighted that the Al Qaeda threat remained significant – with self-radicalised "lone wolf" terrorists of prime concern.

He added: "Al Qaeda has gone from the idea of spectacular attacks to the type of approach where individuals come up with their own ideas and carry them out.

"The capability of a lone wolf attacker is pretty low but we have already seen what can potentially happen with the stabbing of MP Stephen Timms.

"There is now a lot more information out there for individuals about how to carry out attacks and it has been fairly widely distributed," Mr Crump concluded.

The analyst was speaking during a seminar on the 2012 Olympic Games organised by City Security and Resilience Networks (CSARN) in south east London.

Delegates at the event, hosted by Deloitte's, included AC Chris Allison, the National Olympic Security Coordinator and Shadow Olympics Secretary Tessa Jowell.