I've played with this argument with DVSA and bosses in the past.
Let's say you come off a coach at Dover and require a daily or weekly rest. Another driver takes the coach away and leaves you a car. As you are on a mandatory rest you must "be able to freely dispose of your time" as per PSV375. So, what if you decide to dispose of your time by driving home in the car?
Not legal is the response. Now, taking that further, what if you are in a hotel a couple of hours from home on a mandatory 45 hour rest. You decide to "freely dispose of your time" by driving home to see your family. The argument is that this is OK as you can dispose of your time how you want but if you stay there you will break the law as you will effectively be ending your shift while on a rest period. If you visit your family and travel back to your hotel to complete your rest it's legal...