Four of the packages were found Thursday at recruiting offices in shopping areas in Brighton, Canterbury, Kent and Slough, the British tabloid the Daily Star reported. Three arrived earlier in the week at army offices in Aldershot, Chatham and Reading.
Prime Minister David Cameron called a meeting of the Cobra security committee and released a statement afterward. Officials said the bombs were crude but could have caused serious injuries if they had detonated.
"Seven suspect packages have been identified as containing small, crude, but potentially viable devices bearing the hallmarks of Northern Ireland-related terrorism," Cameron's office said. "These have now been safely dealt with by the police and bomb disposal units."
There has been a recent uptick in sectarian violence in Northern Ireland, including violent demonstrations by unionist militants and bombings and other attacks by dissident republicans. Also Thursday, police seized a small stash of pipe bombs at a house in Newry in Northern Ireland after one was thrown at a house in the city, the Belfast Telegraph reported.