Would it be possible to add more information about growing conditions (soil, sun, water, competing plants, possible chemical/herbicide exposure and general region where you are growing - what part of Oz) and to add a photo of the plant in the garden? Also, has this leaf thing been an issue for all the time it has been in your garden or is it a recent occurence?

Ignoring the leaves for now, generally in my garden most clematis tend to not put on very much top growth or bloom much until their third year. More than many plants, clematis seem to need to take time to settle in and grow roots. So the above-ground size alone isn't worth worrying about.

Thanks nhbabs. The plant is in a red silty clay loam, well drained soil of basalt parent material.The aspect is - gets morning sun, but is protected from hot arvo sun. It's been hot lately(early 30's),so I have been keeping the ground moist.The plant is next to a 'corea' and a 'star jasmin', with these two providing protection from the western sun and winds.I'm very careful when spraying around the garden. We are in what's regarded as a 'cool climate' on the nsw Central Tablelands.The leaf yellowing has only been an issue over the last 2-3months(since the beginning of spring)

IME nutrient deficiencies often show up along leaf veins or the whole leaf is pale or chartreusy in color. Looking at the second photo, I am wondering about it being spider mite damage.

thanks again nhbabs,
The appearance of the leaf strongly resembles some photos I've seen of sm damage, but I haven't been able to find any of the little suckers as yet. I'll keep looking!
Ta Macca