I'm just being pedantic here, Gervase, not seeking to make a political point, but there were quite a few "instances of HMG divesting herself of her overseas colonies or dominions without a bit of terrorism". Canada, Australia, New Zealand, most parts of Africa apart from Kenya...
All right there was Ned Kelly, and other small scale equivalents elsewhere, but they weren't the key factor. It basically came down to profit and loss, and most of the time the game wasn't worth the candle. The Empire was largely a matter of bluff.
Ireland's misfortune has been its geography, so close to England.