possibly Crystal Fountain but the flowers are in shade.
Does the centre open out into fine petals ?

Or Koconoe?
but it could be one of others that I haven't come across.

Thank you it is purple with green stripe on petals not sure if the centre opens but looks as if it might! It is not my clematis but one I want to buy if possible thank you very much I will look up the ones you mention 😊

Further to my reply the owners friend has reminded her that the clematis is Taiga which I note is very similar to Kocanoe
So thank you again for prompt reply. (the centre does open a really pretty effect) 😊