Difficult to be sure - colour of stamens is an important part of ID for clematis, as well as flower colour (which I'm assuming was white?) but maybe Chalcedony.

Sorry: no I cant :o)
as bamboo says there are lots of factors to consider.

Your best bet is to go to Taylor's website and do a search using flower colour, flowering time, etc. They have hundreds of clematis, so you'll almost certainly find it there.

taylorsclematis.co.uk

Thats where I found a pic of Clematis 'Chalcedony'...

Many thanks I will certainly go on that website. Thanks again