Via the comment's on Brian's blog, I came across a blog I hadn't heard of before: A National Conversation For England.
Recent posts are all on the AV/FPTP argument, and on the case for a referendum on membership of the EU: all good constitutional stuff. David's posts tend to be long and detailed, and are (as far as I can see) well-argued and grounded in common sense. I'm popping over there later on for a longer browse.
He's on the blogroll, and I will be following what he has to say over the AV referendum with interest.