Baked Sole with Horseradish

I love horseradish and clearly from the way old plantings of it still grow round ancient dwellings it was once more generally used. It is an excellent digestive, but in British cooking its use really only survives with beef whereas in Scandinavia and Central Europe it is used much more extensively. This is a Polish recipe given to me by an old lady in whose Sussex lake we used to fish as children.