they are the fibrous roots of trees and probably still alive that is why they keep coming back. what else is growing on the land?

Thanks."..thought it might be tree roots but how do I get rid of the or stop them growing. There is an old oak tree about 25m away and a couple of ash trees about 15m . If I somehow kill (don't know how) them, presumably this will affect the trees.

Cutting these roots will just encourage more root growth exponentially. Do you have any hedges, shrubs or vines nearby? They appear to be too close to the surface to be from trees.

From the picture I see a Lonicera hedge growing,it looks to me to be where the roots are from.If so then you may need to rethink your planting ideas and go for plants that will cope in those situations.Is the border shaded ? you could try Ferns.Just a thought.

Many thanks to all...it is a small box hedge surrounding the bed, but the roots were there before I planted it. The roots are about a foot down, I have just brought them to the surface when digging. Sleeping on it, I think what I am going to do is double dig the bed, sieve the soil and hope for the best. This will be the last chance. I have planted miniature roses which did not thrive at all, then 3 years later, planted small heuchera plants, but have now replanted those as they were not happy. Now I am going to try heathers. The bed was originally dug around 10 years ago, so feel I have given most things a fair chance, but this is the last chance saloon! Then its back to turf!

Tree roots, I'm in agreement with Seaburngirl - if the Ash trees are very large/mature, likely from those. Wait long enough and they'll die anyway, probably, from Ash Dieback Disease... if they don't, you'll get more roots there, because you're presumably feeding and watering that bed after planting...

I just came across this thread when trying to identify the same exact thing in my own garden. Like Judith, my site was previously woodland and there are still trees alongside my planting beds. These roots are horrible and they are spreading to other areas of my garden. Over the summer, they've risen to the surface and are spreading directly beneath mulch that was laid earlier in the season. Is this the way tree roots behave?

Oh yes, for sure - and if you improve the soil or place mulch, the tree roots will head thankfully for that area - more nutrients available - the purpose of these type of fibrous, fine roots are specifically to seek out nutrients and, more particularly, water or moisture.