The IRA is an excellent example of an intelligent home field advantage against a government. The IRA kept that conflict going for decades. As you said, if they really wanted to go further they could have.
Their final chess move was car bombs in the London City financial district. They set them off on weekends at night to minimize casualties. They wanted political pressure, not to galvanize British resolve with casualties.
ISIS or AQ would have set them off at 0900 on Monday.