SAS team tracked 'Irish terror cell plotting London 2012 bomb attack'

British special forces have uncovered a suspected Irish terrorist cell that plans to attack the London Olympics, the Standard can reveal today.

A surveillance team from the Special Reconnaissance Regiment, seconded from 22 Special Air Service, spent weeks spying on suspected terrorists as they scouted possible targets in east London.

The SAS team, which is working under Scotland Yard's counter-terror command, tracked four men from Oglaigh na hEireann, the extremist Republican group believed to be responsible for the murder of a Northern Ireland policeman this month.

It is believed the ONH cell may also have been spying on possible targets before the royal wedding next week. A senior Whitehall source told the Standard that two known ONH members travelled from Northern Ireland's South Armagh-Monaghan border to London in February to meet two "sleeper" associates who live permanently in the capital. Soldiers from the SRR, which played a key role in preventing the transatlantic liquid bomb plot of 2006, watched the men for three weeks as they photographed key roads and buildings including the Olympic Park and stadium for the 2012 Games.

However, the source said the SRR unit was also examining intelligence to suggest Prince William and Kate Middleton's wedding is also a target. "We believe the high-grade reconnaissance team was looking at possible action during the London Olympics but we have not ruled out the theory they were checking opportunities for the royal wedding," he said.

The disclosure will raise fears of terrorists seeking to stage a "spectacular". It also will focus attention on ONH, which is believed to have planted the car bomb that killed newly-recruited Pc Ronan Kerr, 25, outside his home in Omagh - minutes after 2,000 runners in a half-marathon jogged by.

Oglaigh na hEireann, which means "soldiers of Ireland" in Gaelic, is the most active of the paramilitary groups operating in Northern Ireland and is comprised of former members of the Provisional IRA, the Real IRA and the Irish National Liberation Army.

Its threat to consider attacks in mainland Britain is thought to have prompted MI5 chief Jonathan Evans to warn of the "real and rising security challenge".

Last October, David Cameron's five-year National Security Strategy warned that a new wave of attacks by Irish splinter groups was considered a "Tier One" threat which is the most serious. Irish terrorism expert Ruth Dudley Edwards said: "This shows that brutal, experienced Republican paramilitaries and the young, idealistic recruits they groom for murder are looking to inflict on London what they call 'a spectacular'. Their determination and expertise should not be underestimated."

Established in 2005, SRR conducts a range of covert surveillance and reconnaissance probes across the world, although its primary role is to prevent terrorist attacks in the UK.

The SRR includes SAS troops serving on attachment and forms a team of about 50 special forces that have operated in London since the July 7 bombings.

One of the SRR's first assignments was the botched surveillance operation of Jean Charles de Menezes, the Brazilian electrician shot dead by police in July 2005. One of the SRR team, known as "Frank", admitted failing to video Mr de Menezes as he left his flat because he was urinating into a bottle.