Whatever happened to the golden rule of looking after your subordinates meals, mail and money?
The treasury figure of 40p per mile has been fixed for years, despite spiralling fuel costs, vehicle excise duty, servicing costs.....
However, considering fuel costs alone, I get about 27 mpg because I don't drive some diesel grotbox. That works out at 5.94 miles per litre, or 0.17 litres per mile. Even with fuel at £1.30 per litre (thanks to the thievery of nuLabor), that works out at 22p per mile.
Of course there are other mileage-related costs to consider, such as tyre wear, servicing and perhaps insurance. So your new rate will barely cover fuel costs if you drive anything half-decent, particularly if your commute includes a substantial element of urban driving.