Campanula persicifolia (Peach-leaved bellflower): Tall spikes of large, cup-shaped blue flowers over slender foliage in mid-summer. To 1.2m. Hardy

Centaurea montana (Perennial cornflower): Large blue flowers in early summer, repeated later in year if cut back. Very attractive to bees. To 50cm. Hardy

Nepeta 'Six Hills Giant' (Catmint 'Six Hills Giant'): A vigorous sun lover which will soon make a generous clump. Spikes of tiny purple flowers over aromatic grey/green foliage.