There are all sorts of nuances here, but you use the word partner, are they legally married? If not are they living together as husband and wife but temporarily separated because he is working away in the army?
If he is simply working away absent for less than 52 weeks he is part of her household and their income is aggregaated in the usual way for a married couple. The applicable amount will be that for a couple (HB Reg 21(2)(b)
For HB they are not treated as a couple after 52 weeks, but there is no equivalent time limit in Reg 8 of the CTR (Prescribed Amounts) (England) Regulations.
As far as the actual Council Tax liability is concerned, it may well be that he could be liable (See DONCASTER BOROUGH COUNCIL v. CORPORAL G STARK and SALLY STARK [1997] EWHC Admin 977 (5th November, 1997)
