My clematis is just a bit lacklustre - any advice?

I think that, as they're clematis, they'd do better with sunshine on them. And the flowers don't last that long on nearly all plants - max 2 weeks, often less than week. That's why I don't choose plants for their flowers, with one or two exceptions! I also think you need a better support system so they can scramble up themselves - a bit of clematis mesh pinned to the wall would help.

i think you would see a vast difference in them if you add some sunshine..

I think sunshine sounds like the answer - although today it has turned itself off. Will need to move in to garden. Currently in 3 pots. Ok to move now and maybe in to theground itself so i can put more towards the wall so they can climb easier? Pots or ground? WHat you think? Sandy, neutral earth here.

Seeing as they are against a plain white wall, have you not thought of planting a shrub or self supporting firethorn, which would give you evergreen all the year around, flowers and berries and something for your clematis to scramble through as that is what they like is a host plant. if you have the room for this, then choose one that needs pruning at the same time as the clematis that you can keep both in controle as to the space you have, especially as the clematis have a short flowering period. Choose a host that you can keep trimmed flat against the wall.

Clematis Armandii is an evergreen clematis that likes shade. If you do move these 3 to a sunnier spot, don't forget to underplant, eg geraniums, as clematis' like their roots to be kept cool.

With Clematis that aren't thriving... feed, feed, feed. Water with liquid feed every couple of weeks all summer.