This grower is sure of this plant identification.
This is a dwarf buddleja that has a rich deep purple flower, grows to 120x120cm. I have a few to offer with good roots although the snails have been at the leaves. And yet they are flowering!
Buddleja genus (Butterfly bush). These are deciduous, semi-evergreen or evergreen shrubs and trees. The leaves are large and pointed; they are usually in opposite pairs. The flowers vary in colour and are fragrant, small and tubular.
They are fully to half hardy, and will require full sun with fertile well drained soil. Suitable for a mixed or shrub border, they are generally easy to grow. Prune hard in winter to control shape.
Clusters of small, often fragrant flowers which are attractive to butterflies. Suitable for coastal conditions.