Posted: 19/07/2013 at 17:39
Is the soil soggy? It may have been overwatered.
More likely, perhaps, is vine weevil.
Have a dig in the pot - if you see fat white C-shaped maggots with a dark head you have vine weevil.
Corrently, it can be treated with Provado Vine Weevil Killer, which is a water-on solution.
Unfortunately, the roots have often been eaten away too much by the time you find it - is there any piece of plant still healthy enouigh to take a cutting from?
Finally, check that slugs haven't stripped the bark from the stems at ground level. This happens with clematis.