An i.d on this please

I cleared this border out last year as it was full of weeds. I transplanted most of the bluebells. Then put a membrane down covered with bark and replaced the rocks. The soil was full of other bulbs but I left them as I didn't think they'd come through the membrane.
Lo and behold after a few months the plant in the photos started to poke through and have covered the whole area along with some bluebells this year. I don't mind as long as it's not weeds.
Any idea what it is?

Thanks in advance.

 

Is it an alium .....

 

Looks like Allium triquetrum.
The stems are trangular in cross section.
I believe it is almost impossible to eradicate.

https://www.google.co.uk/search?q=a...ved=0ahUKEwip44_x9LvMAhXrDsAKHXV0BKUQ_AUIBigB

http://www.downgardenservices.org.uk/threecorneredleek.htm

 

Makes sense. Thanks. We sometimes get a whiff of garlic.