Hi
While they are hardier than most tree ferns .Temps much below freezing will probably be fatal. If the ground actually froze I'd say it's gone.
Should definitely be up and growing by now gary

Avoid putting debris in the crown or water in the crown. It's a good way to develop the fatal Rhizoctinia disease.

I have two tree ferns which were starting to shoot when we got that icy blast last April. The new growth was obviously burned black although the plant did try to grow these blackened stumps. All I have now is two plants which are looking very sorry for themselves, with the remnants of the growth in 2011, which I had left until they are now totally brown.

Have I lost them do you think, or will they surprise me and 'regenerate' in the spring? We live in Cornwall which is pretty temperate and am hoping to take them with me when I move.

Reading a post by footfullofbindis, they would appear to be pretty indistructible......but I'm unsure... I have had them 8 years and they have survived happily before.

In habitat they go through bushfires and drought. But usually they're in a more protected place with constant dampness around the roots. Taking that long to recover doesn't look good. From what you say they've been through one summer without any signs of recovery. It'd be no problem to wait until your next summer and see, but I wouldn't be overly hopeful. It's surprising that in Cornwall it'd get cold enough to get that much damage, they do grow at higher altitudes where there's snow.

I had some luck with putting "dead" ferns in the hot compost bin. They begin to grow again and can be replanted later. The heat is like a spa for ferns.