The USA's shadow national security advisers Frederick W. & Kimberly Kagan writing in the Weekly Standard --
Above all, al Qaeda does not see itself as a terrorist organization. It defines itself as the vanguard in the Leninist sense: a revolutionary movement whose aim is to take power throughout the Muslim world. It is an insurgent organization with global aims ... In this respect, al Qaeda is very different from terrorist groups like the IRA, ETA, and even Hamas. Those groups used or use terrorism in pursuit of political objectives confined to a specific region--expelling the British from Northern Ireland, creating an independent or autonomous Basque land, expelling Israel from Palestine. The Ulstermen (sic) did not seek to destroy Britain or march on London; the Basques are not in mortal combat with Spaniards (sic); and even Hamas seeks only to drive the Jews out of Israel, not to exterminate them throughout the world.
It's very hard to fit the Brighton Bomb into that narrative.
Note by the way that the Brighton Bomb unintentionally spawned one of George Bush's favourite War on Terror catchphrases.