Per diem tax arrangements are negotiated by each tax office where a company's head office is based, on a company by company basis,usually one district will treat all companies the same but not always.If you are lucky enough to have your company in the right tax district then you pay no tax on per diems,I get £60 per duty day at Tag which is not taxed at all. Others pay tax on a proportion which is at the whim of the inspector of the district.There should be a national arrangement so that all companies are treated equally,there are mutterings from HMRC that this will happen eventually,if your company's tax office claims there is such a national arrangement they are bull****ting your company just to make them go away.