Well it would be wonderful if such a plant existed, but unfortunately, it doesn't. There are lots of clematis varieties with the colour flowers you mention, but they are not evergreen, and they're not particularly fast or slow growers. There are evergreen clematis (C. armandii, C. cirrhosa 'Freckles'), growth rate average, but they flower late winter or spring and are in the white to yellow range.

Many thanks for your comments, thought it was too good to be true. I have a Clematis Armandii and Montana elsewhere in the garden but just wanted one to cling to an arch next to where a laburnum and lilac are flowering, hence would have liked a clematis which would flower when those blossoms have faded.

Reading your request both ever green and the colours your after but an added bonus of scent smelling,

I would ask you to take a good look at the honeysuckle plant,
this is there all year round and flowers from late may-june through to september.

There are plenty of clematis which flower from mid summer or late summer onwards in the purple range, but they are not evergreen. Have a look at any in the viticella group (Jackmanii, Gipsy Queen, Etoile Violette) or for late spring through summer, Mrs. Cholmondley, The President, Violet Charm, Xerxes/Elsa Spath.

I have an arch which was smothered in honeysuckle within 3 years. It is more or less evergreen and looks good all year. I realise you want a clematis but just thought I'd reinforce what Dungy said! Maybe you could combine honeysuckle with a clematis macropetala which is certainly not evergreen but has lovely decorative seed heads to follow the flowers.

I want to thank all of you for your suggestions - certainly worth thinking about. Probably spoilt for choice now!