Looks like an an Allium to me, but I'm no expert so I'll stand corrected if it's not! Wait till the little flowers on the main ball come out and check out Allium pictures online.

Looks like an allium to me too. By the height I would say you have a nice purple one on the way, be it a bit late? The leaves will start to die off before it flowers.

Certainly an Allium and very like the one I am waiting on, to see what it is when it finally opens. Like you I do not remember planting it.

it looks like a leek coming into flower. I have several that never got picked. wether they are leeks you will have to wait and see. Definitely an allium however.

Allium, as to which - not a clue!

Welcome to Goy. I think at that height it could well be a leek which has gone to seed but if so you would have been aware of it before now I think. They are members of the allium family and you can collect the seed and plant next year. At over six feet it will be interesting to see what size the flower head is when it comes fully out.

Thanks very much for those comments - it's solved the mystery - but I've no idea where it's come from!

Discovered to day there is a 'giant' onion! So maybe it is that.