Jack,
It just occured to me that you should add a fuse.
You could add one straight after the diodes D2 & D5, you could use an axial 1A quick blow, or a resettable fuse.
Just thought it would be a good idea to protect against short circuit, wouldn't want to pop the batts.
Fuse added, new schematic drawn, haven't double checked it yet.
It might be a while until I can get much done as I start a new job tomorrow, which means I'll be working away during the week, and then there will be a house move.
I'm still on it and I'm still very thankful for your help - I will get it done, just not sure on the timing.
Now worries about the delay - I'm still very thankful for the design. I'm the one who should be sorry for not getting on with it but you know how it is!
It looks like I'm not going to be moving house soon and the project will be packed up for the duration - sorry about that, we might see some movement in the new year.