mileage from home to office

[tjl]

My current employment contract says I am office based but, following a change of role, I've just calculated that I only travelled to the office on 66 days during 2017 - 5.5 days per month. If I managed to persuade my employer that I should change to a home based contract, do you think that I could get mileage paid to the office without getting into hot water with the tax man, given the clear majority of the time I'm working from home or travelling in Europe ?