Read more: IRA dissidents pose threat to London Olympics say security chiefs

Counter-terrorism teams in Britain have been diverted from tracking Islamic terrorists so that they can focus on Irish Republican cells operating in the country. The royal wedding on April 29 and the London Summer Olympics 2012 are believed to be possible targets.

The teams claim this is the first time in over a decade that IRA cells have been in operation in Britain.

According to the “London Times,” an attack is "not believed to be imminent" but security agencies and MI5 and Cobra (the British government's emergency committee) have increased the frequency of their meetings to three times a week.

The report says, "The security situation is, according to one source, incredibly tense, with discussions taking place at the highest levels about the terror threat.”

It is believed that the threat is coming from a group called Oglaigh na hEireann (Soldiers of Ireland). However, multiple dissident units are not believed to be in operation in Britain.

Patrick Mercer, a Tory MP, said that the police and army intelligence groups are now concerned over three splinter groups operating in the country.

He told London's “Sunday Express,” "'The timing of the royal wedding seems curiously close to Easter when Republicans will be looking for an excuse to act or demonstrate."

However, the former head of royalty protection, Dai Daves, said that the biggest threat to the royal wedding will be "anti-establishment protesters."

He said, "There are four elements to be worried about: Al-Qaeda, extremist IRA splinter groups, nutters claiming they want to marry William and the left-wing anarchist element. It's a very complex policing situation."

Hugh Roberts, the Olympics minister, also told the “Times” that Irish Republican groups are regarded as the most real security threat to the Olympics which will take place next year.

Read more: IRA dissidents pose threat to London Olympics say security chiefs