Furious is a good way to describe it! It blasted out the top of the airlock & pooled yeast sludge all over the lid the first night. Cleaned it up and replaced the airlock with another (sanitised) one. Did the same again on day two, and day three. It finally calmed down enough after a week, and the airlock stayed clear (though busy) after that.
Added the hops to this yesterday, after a fortnight's fermentation, and down to 1.007. Decide to dispense with the bags so made a hop tea with the pellets (which instantly turn to mush) and put that in. It smelt good before the hops and extremely good afterwards :) That seems to have kicked off fermentation again, as it was bubbling rapidly again after a few minutes. I'm aiming to bottle it on Wednesday.