They sound like scale insect, Paul. I don't have personal experience of these, so I hope someone more expert than me can advise.

The only sure cure for scale insects that I know of was banned a few years ago. Perhaps meths might be worth a try. Or even if you can manage to get the stems down without damaging them you could try drowning them in soapy water

Provado should work. I have also used a combination of carbaryl and surfactant to good effect, but that not on Clematis.

Thanks all,

Now I know what they are Ive been able to search tinternet for options - seems like its S&S for me - scrape em off as much as poss and spray em.

Thanks goodness I got the mix your own version of Provado - its the gardening equivalent of domestos...