Success!!!
After a bit more testing, a lot of head scratching and a little kicking myself I found the problem and fixed it.
The moral to the story is not to make assumptions. The circuit is connected at the junction marked below - usually I'd expect this to be marked differently so assumed it wasn't connected.
Screenshot 2019-11-02 at 15.06.46.png
Adding a small link to the circuit as below and it works like a charm.
IMG_7528.jpg
Now I can move on to building this into other projects. For anyone else looking to do this then at least I've validated the above circuit diagram so you don't have to.
If it's any help I can post the Eagle files for my little prototype circuit - just let me know.