I can't work out how giving us tax-free pay would be such a difficult issue. F&CO CS personnel have been tax-free overseas for years.
Perhaps that'd be a little too good for the officers (well actually anyone who earns over about £26,500, so that'll be Cpl's with a few years in post) for a Labour government so desperately trying to turn red again after a few years being ever-so-blue.
Solidarity brother.