In your latest post you ask:
18/19 is a year of residence and it is this year that may qualify as a split year.Also, seeing as one becomes non-resident when they leave the UK to live and work full-time overseas, haven't I become non-resident in the UK for tax purposes again? Is this correct?
As I indicated in my earlier post it seems to me that only Case 4 is capable of satisfaction.
With respect to your above query, Case 1 which deals with an individual who leaves the UK to work full-time overseas cannot be satisfied by you.