I can only think of the small flowered montana type, they are vigorous and hardy and may work

I found this info. on the British Clematis Society page:

All alpine, macropetala and tangutica types and the following large-flowered cultivars:

Bees Jubilee Carnaby Dr. Ruppel Guernsey Cream Hagley Hybrid Henryi

will grow happily on a north facing wall. In fact, the flower colour is best preserved when not exposed to bright sunshine.

Hope this helps you to choose one ( or more!).

Thanks Pamg I do have a couple of C. Montana clematis in the garden and dismissed using one as they are so rampant, but thanks for your suggestion.
Thank you also to Shirley tulip for the great assorted list of Clematis you found that will grow on a North facing fence. I am sure that I will find one from the list that I like. I will post the one I choose on this forum when I finally make a choice.

Hagley Hybrid (which someone's already mentioned) and Nelly Moser do much better in a north facing position - the colours fade too quickly in sunlight.

Thanks for your input Bamboo, much appreciated.:)