The above has been in my garden for several years. I have always treated it as a weed but ....... it isn't an ugly plant and has a unique and not unpleasant strong scent.
I have looked on-line for a matching picture and, whilst there are one or two similar - none seem to match exactly. It produces pink / purple flowers during summer and spreads indiscriminately - however, it is very easy to pull up.
Any advice / information gratefully received!