Keeps coming up this one
There are, or should be 2 x rates in your portfolio
Rates you charge your customers
Rates you charge trade
Rates you charge customers can vary from 80p per mile (for those that like racing around being busy busy busy but with very little business acumen) to £1.50 per mile (for those that like sitting around doing diddly squat for most of the day happy in the knowledge that when they do move, they're taking the piss out of whoever it is they're working for).
Most of us are somewhere inbetween the 2
Trade prices vary even more than that, depending very much on where you are, where you're going, and where you want to be
Some have the same rate for both 1 and 2, and some see the sense of trying to maximise their profits and/or dead mileage by offering a "reduced"rate
This will vary but will be anywhere from 50-80p per mile.
Happy hunting