Gainesy,
I hope by 'they' you meant MPs
.
The civilian clothing allowance is for 'other ranks' only - presumably because they are all working class oiks from sink estates and would otherwise turn up in tracksuit bottoms and singlets. Officers, who are all scions of the landed gentry with private incomes and no chins, have to buy their own suits, just like they have to buy their own uniforms.
BM