It's useful to solve the theme before attacking the code. To solve the theme it might be worth considering why the setter used the strange word at the end of clue 24D.
I'll post a comment on an 'answers' thread in a few minutes which might give a little assistance in breaking the code.
Lastly, though I fear not the last time that I will need to repeat this, Ulster does not equate to NI. Maybe if you live in Surrey or Herts you are indifferent to these matters, but by making Ulster = NI, you are depriving the citizens of Donegal, Cavan and Monaghan a province...