Sorry haven't had a chance to get on the site for ages with work and weekend spent working on the house (see my other couple of posts today!)
We've finished the wall project - choosing to open the whole space up, while keeping the lower part of the wall for the radiator, and a floor to ceiling post at the end for stability. We've plastered, and clad the cut edges with stained timber (looks a lot nicer than it sounds, honest... although we will probably remove the couple of screws we did need, and use the dowel trick that was recommended above. We've exposed the floorboards as well so the whole space looks a lot nicer