Posted: 29/07/2017 at 14:30
It looks more like a honeysuckle than a clematis. Honeysuckles twine around their supports as yours appears to be doing, whereas clematis use their leaf stalks to cling onto things like this
My guess is that your honeysuckle is very thirsty ... they need a lot of moisture and as it's at the foot of a wall it's probably shielded from most rainfall (what we call a 'rain shadow') . I would give it a bucket full of water at least twice a week from now until autumn, whether it rains or not. If you can get hold of some well rotted manure, leaf mould or home made compost mulch around the root area with that (just don't have manure actually touching the stems ... leave a small gap)
Next spring water it the same from early March onwards. and also give it a sprinkling of Fish Blood & Bone (a slow release organic fertiliser) in the spring.
Let us know how you get on