Err, soft shield is a lovely fern (imo)

I especially like the selections from the plumosomultilobum group, as the fronds take on a curving, layered appearance that looks like a giant spiral!! Extremely handsome ferns with scores of very architectural and quite disparately appearing cultivars.

It's very much more likely to be a young Dryopterx felix mas, Male fern, which commonly appears in dampish spots in gardens, often appearing with harts tongue.

Young being the operative term, with these not having characteristic adult foliage on display yet.

Thanks to everyone who responded! I'll keep an eye on it and see if it changes as it grows - I had wondered if it was a juvenile form of something, so will be very interested to see how it turns out.