Is it in a pot or planted outside? My one which is planted outside just spreads & spreads, though some of the soft new growth got blackened by those frosts last winter, it just grew up from the roots again. It is growing in a shady place, sheltered by a Holly. What is the problem with yours?

I have several in the garden and i noticed new ones growing in the wall. They are just left to the elements in partial/deep shade. They are a hardy native fern.

The tropical species grown indoors do best in a bathroom with a large window, a skylight, or solar tube(s). They like bright indirect light and fairly high humidity. Soil should be well drained, but water retentive--African Violet mix is ideal, in my experience. They should be soaked often enough that no more than the top 1/2 cm of soil dries out. Any good houseplant food will work, but mix it 1/2 strength, and put it on twice as often.

this is a case of needing to know its scientific name to be certain which one you have pennyfarthing. Can you adda photo of it?

I have inherited this plant from my cousin who has moved into care. It lived in the disused fireplace in her living room and always looked wonderful.
Now a lot of the fronds have gone brown. There are a few spindly little fronds in the centre but it is looking generally weaker. I have it in a north facing room. I don't know whether it is a hardy fern or a tropical one. Maybe humidity is a factor and I could try repotting it with an African violet compost. Thanks Tug.
Sorry SBG I don't have much luck loading photos. I would love the fern to be hardy and live outdoors but don't want to risk it! I have to say, Feverfew and Seaburngirl, I have always thought these ferns were very fragile and didn;t realise they could be hardy in our climate.
Thank you all for your comments and advice. I do hope I can keep it going.

I think that repotting it might be a good idea or giving it a feed of Babybio or something similar. It has probably been in the same pot for a long time & has used up all the nutrients.

Thank you, Feverfew. I will do that.