Expenses for nights on Agency work

just been talking to tax office,spoke to 2 people one said yes one no,so they are going to ring back.It seems if you are not self employed and go to diffent companys you can claim mileage at 40p,if you stay at 1 company like me you are classed as permanent which is why they don’t no what to say,if im permanent i should no when im working but i don’t and only done 10 days this year,so will tell you when they tell me.