Well of course he wont serve the full term - they almost never do - but the driving ban should still start the day he is released, not be served whilst he is in prison and not driving anything anywhere.
If the four year and ten months driving ban started after he was released from prison (and after passing another driving test), that would make some sense - but I doubt the legal system's got that much sense.
There's no point in a driving ban whilst he is in prison, when he won't be driving anyway.