Autumn prune clematis?

Helen Yemm said "late flowering clematis, the popular viticella hybrids, Jackmanii and so on, can be cut back in the autumn". I also remember Monty Don saying this somewhere. I know my Etoile Voilette is a viticella and last year I did this and then cut it to the ground in spring as well, and it flowered well as usual. I'd like to do this with my other clematis because they look so scruffy in winter but what is a "viticella" and do any of my other clematis fall into this category? Piilu Little Duckling, Niobe, The President, Dr Ruppel, Forida Sieboldii. Thank you.
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http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=347 clk, try this link to the rhs website.
You can look up your clematis on this site - http://www.clematis.hull.ac.uk/ - using the text search facility, and that will tell you the pruning group. Any in group 3 can safely be cut back now to tidy them up and then pruned back hard in spring. Best not to do the hard prune before winter as leaving some top growth on means those stems take the frosts and the crown and base are protected.
"We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
Sorry Dave and obelixx, I thought I'd posted a reply thanking you for your responses but it seems to have vanished. So, thank you. For anyone else viewing them, the RHS link doesn't seem to say much beyond the usual 3 group pruning advice but the Hull website is brilliant for all aspects of growing clematis.