A few more clues would have been useful, such as when and where was this picture taken, is it flowering now, and a close up. Can't really tell what it is, too far away without more info, could be Perovskia but looks too green leaved for that, otherwise some kind of Veronica or Verbena.

Possibly Chaste Tree--which can be grown as a die-back shrub in the UK. I would need a close-up of the leaves to confirm or deny.