What am I?

I saw this lovely flower on the side of a field........it looked like it was scrambling through a Willow-like tree and was only in this one spot. I've never seen it before and it reminds me of a Clematis but has much much smaller blooms ( these were about the size of an average bumble bee).........any ideas what it is, anyone?
It has been overcast for most of the day but dry with a few sunny spells, so can't really complain however, it has turned horribly humid again and the grass is turning brown, so I think we need a sprinkling of rain ( but not too much please, Mr Weatherman) :-)