@Drellingore....what happened in the end? Did you build or go for full planning? I'm finding it difficult where some authorities are flexible and others are not. Did you succeed?
Was it straightforward to get full planning? I have something similar, Class Q permission already granted a year ago. But reality is that most of it would be new if converted. Not sure what to do next. Is it just that the planners are happy with the profile of the building and barn aesthetic?