Firstly thank you for everyone for some very well written and decent replies.
I would certainly be qualified to teach ground school considering my Aviation background outside of flying. This is something I would consider, however as pointed out the flight training industry is going through some hard times at the moment and these jobs are rare.
I am not employed by NATS, but I do something similar and my employer views my Instructors rating as a valuable asset and has no objection to part time FI work.
I understand that living off a full time FI wage is a sacrifice that many make and I admire that, but I have financial responsibilities which I must keep and cannot forfeit at the moment. I think the best thing to do for now is to market myself to flight schools during the build up to summer as a part time FI who has lots of availability and can be at the airfield at short notice!