An officer has a standard tax relief of £367 pa (well it was) which is deducted from his gross pay (her allowance is greater, about £418 iirc).
Pontius: the female officer tax relief was not to my knowledge different from the male one. Female officers never received the 'hosiery allowance' that the female troops did. Incidentally, I understand it has been removed this year.
No, I haven't suddenly started wearing hosiery to work (that you can see), but the Marines I worked with thought a hosiery allowance was a top idea.