This grower is sure of this plant identification.
Royal Fern. Magnificent deciduous fern with very large fronds unfurling from a woody hairy base. Tall "flowering stems" appear in the centre of the plant. A mature specimen may easily attain 150cm in height and spread. An iconic waterside plant in a sunny position besides a pond or stream. Award of Garden Merit.
Royal fern, Flowering fern
Osmunda regalis (Royal fern). It will grow to a height of 1.8m with long bipinnate fronds.
These are very frost-hardy ferns and will require a position in shade with moist, fertile, humus-rich soil.