Also it's not just whether you get the letter from your boss and you have a valid case for getting one. If they (the plods) can see that you can do other duties at work that don't require a license then they won't give you one. And if the plods are having a bad day.... forget it.
And don't get caught speeding, dd or anything if you do get one, a friend did, and he's up for a year, no if's, no buts.