What's this wildflower?

Update - I reckon this is lady's smock or cuckoo flower (or Cardamine Pratensis).

Not the most imaginitive title, but I've tried various websites and haven't come up with anything - tell me if you know. I spotted it on a lovely walk with T, starting at Peebles and walking north towards Eddleston along the drove road on the west side of the main Edinburgh road and then crossing the valley at Nether Kidston and climbing up the track to Collie Law and returning via the forest track. It was a great day, sunny for most of the time but with a welcome breeze. And it was a tougher walk than I'd done for a long time, but I made it - and I'm not crippled today! (Backblipping from 20th.)