They naturally grow in watermeadows. One of the best places to see them growing in the original condition is in a watermeadow alongside the Cherwell river in Oxford, which lies within the (very extensive) grounds of Magdalen College. It regularly floods in winter. The soil is, er, clay. But they have also spread onto grassy banks above the floodline, so I don't think they rely upon being underwater. But they do need it damp in the winter.

I would imagine the difficulty of growing them in pots is keeping them sufficiently damp in winter without getting frozen or being waterlogged and going rotten.

My grandmother used to grow them in her moist soil in NE Cheshire on the edge of the peak district, so I don't see why you can't grow them in the ground in Cumbria, provided the ground it is sufficiently water-retentive, and drains adequately in the summer.