Alright - I've dealt with Apple support on this issue - THEY WERE NOT AWARE OF THIS ISSUE AND THEY BELIEVE IT TO BE A HARDWARE ERROR.- SO THERE ARE NO PLANS TO FIX IT IN ANY UPCOMING PATCH AS YET!
After trying a number of troubleshooting measures - even a complete reformat to factory settings - the issue was still present.
I sent Apple my iPhone 6+ to investigate the problem (I chose not to go through my provider, Vodafone - I figured that would only take longer and they would be a worst case scenario if needed!) - they had my phone 2 days before sending me a brand new (unlocked) phone with the following statement;
"Thank you for choosing AppleCare Service. To ensure the higest level of quality and reliability, all work has been performed in an Apple approved screening facility. After thorough diagnostic testing, it has been determined that a replacement iPhone (enclosed) is necessary."
So - there you have it folks. I got a new phone and it's working perfectly so far. I suggest you contact Apple directly to sort this out.
I hope ye still have your previous phones - you'll need it for about a week! 🙂