[MalcW]

It's growing right on the edge of our plot, and is a bit over a metre tall. Do I want to keep it?

Thanks.

[mumofstig]

looks like a mallow to me, pink or mauvey flowers - either the wild one or a garden escape.
Don't let those seeds go everywhere  although 1 or 2 may be nice, they do seed everywhere!

http://wildplants.wordpress.com/2010/07/08/common-mallow-malva-sylvestris/

[MalcW]

Hi MOS, Yes, I think you are probably right. Based on your link; I think I'll leave it there and treat it as a medicine cabinet. I'll keep an eye on the seeds though.