As regards last para, Steve, indeed! And I suspect that's why mine is lined - it was done in Feb 2008 (after a rather chilly winter). As far as I recall, it wasn't specifically that I had it lined, it was that I wanted a stove installed & Cliffords' (excellent folk if you're in a generous radius of Wisbech) said "That isn't lined, we'll have to line that", to which I said "fine" because... The bummer was that they could only get a 6" liner down it because of the bend at the bottom - one size too small for a stove with a back boiler! You're right in that A smoke-tight chimney flue in sound condition doesn't need to be lined, but if you don't run a hot flue, deposits can easily soak in (through cement more than brick, I presume). I presume that's what happened to mine ere I bought it. That won't happen with a lined flue.

And you're right - it was jackdaws, rather than rooks. I've no idea why I wrote rooks, I do know the difference! I seem to remember we've also disagreed over Stovax (I don't run a low fire, as you may gather; from my point of view it just makes the sweeping easier), but at least we agree that the hotter the fire the better! ;-)