Difficult to tell really...my first thought is that I could be purple loostrife (Lythrum salicaria)

What's the second question ?

I thought loose strife as well.
I'd wait till it opens, and then decide if you want to keep it. It might be a very pretty flower :)

Thanks guys I'll ask the owner of the garden what they want to do, under the circumstances.

Could be a willowherb. Whether or not it is a weed depends entirely on your thinking - one man's weed is another man's wild flower.

Patfran; You're quite right...definition of a weed? A plant where it shouldn't be. Definitely not a Willowherb and I've spoken to the owner of the garden and he says to dig it out.