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They have something to kill for. They have the numbers: 3,000 on the MI5 list, and 20,000 on the broader list of which the Manchester bomber was one. Access to bomb material is moot, as they often go for different ways to cause death.
Terrorist is a meaningless coverall, the Irish Republican Army, the killer of Jo Cox, whatever you want to call the muslims inspired to attack the west, but I'd say these are closer to the IRA than some random nutter.
But don't the jihadis resemble the IRA more than "angry white dudes who want to go on a killing spree"? And that took a longer time to play out.