Pink flower

I haven't strayed far from home today, just enjoyed a nice quiet Bank Holiday without leaving the grid square. Put up my bean poles and planted out the sweet peas. I did take a walk to the woods to look at the bluebells (now at their best) and I saw a redstart (I didn't know that's what it was, just watched it singing a lovely song and looked it up in the Bird book when I got home). I also looked up this pink flower which was growing on the verge, but it's not in my wild flower book. Any ideas?