Feather palms (any) are simply not hardy in this country unless you live on Tresco etc. There are two fan palms though, Trachycarpus fortunei and Chamaerops humilis that are relatively hardy.

Sadly for you, I suspect that you're two plants are dead. There isn't really anything that you can do to change this state except wait and see. In pots also, they will almost certainly had their roots frozen also which doesn't help their predicament.

In the centre of the country where you are also, you can get pretty cold winters compared to the coastal strip around these islands which counts against their return and of course, this has been the worst winter for a long time.

Sorry!