Sounds like it could be wild garlic and they get everywhere. You could try a systemic weed killer when, they have grown some leaves, otherwise its going to have to be the hard way - dig them out or pull them out.

Yep, I agree, it's wild garlic, which has pretty white flowers in May. Leave a wee patch and use the leaves in salads and soups, or wilted just like spinach. Yum.

I'm not sure, but I think I've heard it was introduced by the Romans so it's been around for a very long time! Do you have any old woodland nearby? Some of the woods in the Sussex Weald have lots of it. I can see why you wouldn't want it in the garden---scent is a bit overpowering!

Thanks folks. The only trouble is it's smothering bluebells and new plants that I put in last year and a strong weedkiller would kill everything!

Wild garlic leaves are quite broad, and the wild onion ones are more grass like. Both will spread but the garlic smells a lot stronger and smother stuff more quickly. Remedy for both is the same though, patient digging out. You nay find a slot where you could spray after the bluebell leaves have died back though.