It sounds a bit pretentious to talk about the characters I've created having a life (and mind) of their own. Certainly before I began the Edith Horton series I would have seen this as a fey and airy-fairy idea. In a "laugh at yourself before anyone else does," view I would have dismissed the notion. I reckon this has a lot to do with the upbringing you have - not only your family but the whole package, school, area etc. Heck, maybe even culture & country!
So, it is surprising to me that Edith and her friends & family have gone off in ways that I hardly recognise. It is a process, I suppose and maybe it is one of the reasons you, as a writer, keep on with a series. So, with Swallow Hall Murder off with the editor (and me waiting, holding my breath) I can only be grateful as it makes the thoughts of writing the next book intriguing rather than tedious.