Solved Large ornamental grass

This has self seeded in a wild patch in the garden. I thought it might be a miscanthus malepartus as I have one, but the seeds are completely different. The new plant's seeds are on the left, malepartus on the right.

It's about 5ft tall. Ayone any ideas what it could be?

 

Hello, it's not an ornamental grass. Sorry I don't know the Latin name (yet ) but it's known as cow grass here...self-sows with gay abandon.
Edited to add...Echinocloa crus-galli

 

Brilliant, thank you!

 

You're very welcome Get it into a dustbin bag and a long way away asap!