On bank of canal.
No interactions present.
Certainly a Common Blue, from the habitat and details visible on the photo. If you look at the original, and zoom in to the top of the butterfly's wings you can just see a glimpse of the upperwing, showing a bright blue colour and a hairline black border. Chalkhill would show a thicker black line and pale blue colouring. And chalkhills never stray away from limestone/chalk coasts or downland.
Best correct the typo in the ID before I give you a spot-on!
I can see why you might think this is a Chalkhill Blue, as there isn't much sign of orange on the underside of the forewing. However, your butterfly is looking a little battered and it always seems to me as if the orange marks are the first to go. Bob's observation of the little bit of the bright blue showing from the upper wing surface is key though. I've posted some Chalkhill Blue images that show the males are far paler and have wider black borders: http://www.ispot.org.uk/node/3760 I also have some Common Blue images for further comparison: http://www.ispot.org.uk/node/2982
Lat/Lng: 51.855343658705, -0.64576864242554
OS grid ref: SP933182