With the deaths of 29 people in the 1998 Omagh bombing, the Real IRA succeeded in carrying out the worst single atrocity in more than 30 years of violence in Northern Ireland.

Four suspected dissident republicans were being questioned by police in Northern Ireland tonight following a ‘‘sting’’ operation during which a sophisticated rocket launcher and warhead were seized.

No terrorist organisation has yet claimed responsibility for today’s car bomb in West London but the Real IRA has been the only group which has attacked Britain in recent years.

The Real IRA has been cracked wide open by an MI5 spy who is set to testify at the trial of the dissident terror grouping’s suspected leader, according to reports.