Whats the 'weed', any ideas?

If you've seen this question before, you'd be correct. New to the forum, and wasn't attaching the image properly... third time lucky!! Any ideas as to what this 'weed' may be? I recently re-seeded with a mixture of poultry grasses, and quite a few of these have appeared... along with many more unwanted guests! It's the plant in the photo with the white seed clusters. Apologies for the poor quality of the photo. Any help is much appreciated.