OK - strictly speaking if you have the 50% uplift provision, and it covers additional income, then one way of looking at this is that you ought to pay over half of the saved monies, however depending upon the wording of the provision - which can often be different from IP to IP or creditors modifications, I would try my damnest if you were my clients to avoid you having to pay over the saved taxes and allowances.
The thing about Armed Forces personnel, which I know from my own personal experience, is you can be quids in if you are serving in Germany (less so these days I know) and really on the breadline if posted to Northern Ireland. So, my gut feeling is to allow you to keep the money, but to insist that it be kept to meet any future income shortfalls and to meet your family's additional costs incurred in you being away from home.
I am sure that both of you are probably having to fork out for essential items of kit which are not readily provided to you, and that your families will need some extra funding perhaps for travel and childcare costs.
In my humble opinion you lads (or ladies!) do a fine job for our country, risking your lives on a daily basis, and I am sure that creditors would actually be very happy for you to keep those saved funds. Perhaps your IP would be happy to canvass them to see what their view is on the telephone - I certainly would do that as a matter or course.
The very best of luck with this, let us know how you get on, and most of all keep your heads down and keep safe.
Regards, Melanie Giles, Insolvency Practitioner