Can I just say that Chris is an absolute gent - he deserves every accolade we throw his way.
He spent time with me this evening troubleshooting my Bolt-On issue via Skype, and
/hangs head in shame 
, we eventually fixed my issue by rebooting the
modem that the Mikrotik router is connected to. I'd bounced the Mikrotik but completely forgot about the modem which is stuck under my desk since all it does is connect to the Mikrotik.
Consumer level modems really aren't designed to run 24/7/365 - they need rebooting every once in a while.
So, for any of you struggling, remember to bounce ALL the equipment in the chain as a first step before asking for support.
@chris, thanks for all the help and for getting the data usage issue sorted (/holds thumbs).,
PS: was a really interesting chat we had afterwards.