Bugle (Ajuga reptans)
One needs to be a bit careful as it looks, at first glance, a bit like Ground Ivy and it is, indeed, closely related. A more detailed look will quickly tell you it is not Ground Ivy, the plant being usually taller, the flowers larger and a darker blue and the stem being darkish in colour, almost a dark red.
Flowering for a short time in May, possibly in to June it can be seen now.
Why it is called Bugle I have no idea, perhaps it is those long 'trumpet like' flowers?