I'm not sure what onion grass is, Jessm. Does this flower - and are the flowers white clusters - a bit like little bluebells only white? If so, I think it's wild garlic, and it's an absolute menace and very difficult to eradicate. I think you'd need a 'Round-up' type of weedkiller, and several applications.

They might be Alliums - I've pulled a load out today and they smell very strongly of onions, but the flowers are pretty, pink, white or yellow.

They look like what we know as "three cornered leek" - Allium triquetrum, AKA wild garlic. We are plagued with it too. If you break a leaf is it triangular in cross-section? The bulbs are quite wet and juicy until summer and the leaves are very lush and smell of garlic. They're quite pleasant chopped up in a ham sandwich, and the bulbs have a sweetish taste if you eat one raw.

Spritz is quite right - it's almost impossible to eradicate, I find that even Roundup doesn't really kill it off properly, the bulbs come back. If you pull it up, it just continues to grow wherever you move it to, and it's too wet and sappy to burn. Quite a problem!

Cooking with it might be the way to dispose of it - I'm sure Jamie Oliver's training restaurant "Fifteen" was demonstrating making something with it when I visited for a Farmers Market last year.

It isn't the wild garlic I know, which has much broader leaves. I think it is wild leek.

There's more than one plant known as wild garlic. I think the one you're referring to is also known as "ramsons" (Allium ursinum), Steragram. That doesn't grow here - there's a dividing line further north in Cornwall. On one side you get this plant, on the other the garlic smell is coming from your plant.

There is also a true grass called Onion grass usually sold in a variegated from, but which reverts to normal green. That is also a real thug spreading by both seed and bulb like roots. Will remember its name eventually too.

another answer to this has been posted today by Steragram, who couldn't find this question to post it here, so either have a look at the questions posted today (its under Questions) or go to Steragram's profile page and select their Question section and read it there.

Thanks for all of your responses! The reason I posted this question here is because I was convinced it was wild garlic and promised to save a large patch of it for a local chef...who then saw it and said she couldn't use it as it's not wild garlic! Other searches on Google suggested it was onion grass...closest thing I could find. It's strange - it didn't flower last year but did the year before...? And then it was little white flowers. Not dissimilar to the wild garlic ones actually...confusing!

Beattie, I just broke a leaf and it does have a triangular cross-section... We're the only garden in the street it's decided to plague.

OK, it's Allium triquetrum then.
You could control it a bit by pulling it out and eating it.

Here are some recipe suggestions -

http://www.eatweeds.co.uk/learn-about-three-cornered-leek

http://www.eatweeds.co.uk/lady%E2%80%99s-smock-three-cornered-leek-salad

http://wildpicnic.blogspot.com/2009/08/onion-weed-allium-triquetrum.html

http://forum.downsizer.net/viewtopic.php?t=11814&start=0

http://en.petitchef.com/recipes/spud-sunday-on-the-wild-side-fid-815986 (recipe for pesto)

Make it fashionable and you'll make a nice little profit if you can sell it to restaurants, farmers markets and so on! :-)

I note from reading the fourth one down, that I'm not the only person who calls this wild garlic (in addition to everyone I know, of course)

Reading the fifth link reminded me that the chefs at "Fifteen"'s Farmers Market were making pesto with it.

No recipe here - just appreciation!
http://www.playingwithfireandwater.com/foodplay/2010/06/allium-triquetrum.html

I'm looking forward to using it more in the kitchen after finding all these. ;-)

Me too! Fantastic, thanks v much. Feel a bit better about it now... :)

It's still a thug though! ;-)