Thanks again for the continued advice guys.
I am considering all my options at the moment, including US based (although the most accessible spots seem to require FAA PPLs and Class 2 certificates).
The option that looks most promising for the time being is to self-certify as you suggested 2close. That would allow me to hold an NPPL, which allows me to hour build in a PA28 until 8th April 2018. That might just save my skin if my appeal is successful as I can continue to progress slightly while I wait for the CAA's decision. I'm just trying to find out if my current medical problems preclude me from taking this route. As far as I can tell, it shouldn't be an issue.
I actually started another thread in the medical forum looking for feedback. Similar to your experiences 2close, I've not heard anything positive about the way the CAA operate either in that thread or from others I've spoken to. It is very disheartening, but I will try my very best to get this sorted prior to my exams expiring. I do agree however that at this stage paying for and beginning either a CPL or IR course (subject to somehow meeting the hour requirements) is probably best put off.
Nothing further from the CAA yet in terms of getting an extension. Will update this thread as soon as I hear anything else.