Well, James, native, or not native, Marsh Orchids in the damp ground around the edge would be my starting point. Just what you plant would depend on wether you wanted the area to be native or exotic. Myself, I would be looking at candelabra primulas, Gunnera and Lychinis (Skunk Cabbage). If bamboos are your thing, then OK.

Willows of all sorts are another thing to consider,they love a really damp or wet area. Most, though, are invasive, as in the coloured bark types (Salix britzensis) and will need to be kept in check.
I wouldn't consider Bamboo a good choice for an area which is as wet as you say - many of the varieties do not like to dry out completely, but preferring moist but well drained soil is not the same as liking a soil with seeping or running water.

I immediatly thought of willow, you could stool or coppice them, if you've a multifuel stove then they could provide fuel

Common Reed grows tall and makes a sound like mature Bamboo in the wind. It might even start to grow naturally in the land you describe. The seed heads are on Reed now is you help yourself to a local supply. They also grow like Bamboo from runners. Horses are unharmed by it. I would not waste money on Bamboo as others have said as it sounds too wet. Willow will do well as does Scots Pine. My worry for both of them is the knee high water in winter. Skunk Cabbage is a good choice, again it may grow by itself as it is colonising UK waterways.

Thank you all once again.
James