I think the flower colour is white just the camera didn't get the balance right. It's most certainly not Angelic or alexanders both of which have green/yellow flowers but a very different leaf form. If it were in my garden here in Denmark I would say it was cow parsley, what does the bottom of the flower look like? are there any bracts under there? is the stem hairy or smooth?
Whichever one it is there is no need to be suspicious of it just don't eat it. and probably don't let it seed unless you want an entire garden of the stuff.
Thanks for the replies.
I'll have to check for bracts on the flowers and hair on the stem, next time I'm over there.
I worry about it being some like giant hogweed, my mom isn't up for policing the spread of anything dangerous like that.
I'm wondering if it could be hemlock.
Here's a photo of the stem: