Looks like the native Sedge Bernard (Carex) I personally like it, but it can go a bit bonkers and take over, it is a perennial and favours damper conditions

Hi Bernard,
I've just pulled loads of them out of my garden, they self seed every where and do indeed go bonkers and take over!!!!!

Happy gardening.

I agree with the chickenlover - you can keep it if you like, but it seeds prolifically, so you'll be pulling them out for ever. You could remove the seed heads before they shed to reduce the weeding later, ....maybe, ... a bit...

Dig it up, don't let it seed, dispose of without letting any of the seeds fall. Even then I bet you'll still get another one or two growing!!!!! It looks very attractive but aargh! I dug a very large one up many years ago and ever since then have continued to pull out seedlings every year.Grows especially well around our pond.

Thanks for the warnings. I'll have to bite the bullet and bid it farewell. This woodland garden of mine is proving to be very much a lucky dip. I'm always getting surprises, and most of them seem to be pleasant ones, so I can cope with the odd disappointment. So lucky to have the expertise of GoY members to call on, otherwise I'd be totally lost and would have to resort to weeding out every new seedling that appears, taking a great deal of pleasure out of my gardening experience. Thanks again for your help and encouragement.

Can I muscle in on this question please? Can you tell me if this is the same as Carex pendula, the tall one? I asked my nursery for one and he said they were a pain and gave me one for nothing, but it looks much more like this picture than what I was looking for.