Are there any botanists in the room?

Last week, at the same time as the bluebells finally started appearing in the woods, these pretty little flowers appeared all over our front lawn. It's really peculiar as we didn't have them last year, I haven't sown anything there and nobody else in our street has them!
Any ideas what they might be?

 

 

 

Update: I have been informed that they are in fact the delightfully named "Cuckoo Flower" ( Cardamine pratensis ).  This makes me enjoy them even more, although it still doesnt explain why we are the only front garden on a road of identical houses to have them!