We have found 12 plants that meet your criteria.

hyssop
Agastache 'Black Adder' hyssop Distinctive violet, bottlebrush flowers £7.49 Buy
butterfly bush (syn Buddleja Flower Power )
Buddleja × weyeriana 'Bicolor' butterfly bush (syn Buddleja Flower... Striking bi-coloured flowers £12.99 Buy
butterfly bush
Buddleja davidii 'Black Knight' butterfly bush Sumptuous deep purple flowers £8.99 Buy
butterfly bush
Buddleja lindleyana butterfly bush Ideal for training against a warm, sheltered wall £12.99 Buy
Price Pruned
rose Cardinal de Richelieu (gallica)
Rosa 'Cardinal de Richelieu' rose Cardinal de Richelieu (gallica)... Velvety purple blooms NOW £12.49 Buy
Price Pruned
rose William Lobb (shrub)
Rosa 'William Lobb' rose William Lobb (shrub) Scented, deep crimson flowers NOW £13.49 Buy
lesser periwinkle
Vinca minor 'Atropurpurea' lesser periwinkle Delicious dark damson-purple flowers £8.99 Buy
heartsease
Viola tricolor heartsease A pretty short-lived perennial £1.99 Buy
wallflower
Erysimum 'Bowles' Mauve' wallflower Stunning mauve flowers £6.99 Buy
three species pelargoniums
Pelargonium 'Renate Parsley' three species pelargoniums Masses of small, airy flower sprays £19.99 Buy
New
butterfly bush
Buddleja 'Buzz Lavender' (Buzz Series) butterfly bush The flowers are a magnet for butterflies £12.99 coming soon
New
butterfly bush
Buddleja 'Buzz Magenta' (Buzz Series) butterfly bush Lashings of summer colour £12.99 coming soon