My Clematis book states that the wilt is caused by a fungus, Phoma lematidina, entering a damaged part of the stem. The point at which "wilt" affects the plant is generally near soil level. All affected stems and foliage must be removed and burnt. Any remaining stems can be sprayed with Bio Supercarb as a possible preventative measure against further damage.

Hope this helps you Phloxie.

Thanks for your helpful reply Shirley Tulip. I will buy some Bio Supercarb on my next visit to the GC and hopefully banish this problem once and for all. Phloxie :) :) :)