Clematis are very responsive to being fed well and given lots to drink, much like many of us. They, too, will become fatter, although their health will improve, whereas ours tends to be impaired! Try cutting it back now, giving it a good meal, with drink and a mulch to conserve moisture (as a side order), and see how it responds. 'Edith' is white with red inner bits. Check your label?

I've lost the label, though still have my handwritten list and plan, so it could be MultiBlue, not sure as lost one clematis on that fence.When you advice cutting back do you mean right down? I was just thinking of cutting off dead blooms for now, though happy to follow your instructions.Thanks.