Was there a legal requirement? Well dependent upon interpretation probably yes.
I'm sure it used to be so. I admit to not having got fully to grips with the wording of the requirement under SERA just yet. However, about ten years ago I was reported to the CAA for allegedly not booking in or out at a minor UK airfield. It was an unjustified allegation, because I had been booked in by our company ops dept. and the airfield owner had failed to read his own written log, where I had booked out in person before departure, so no action was taken against me.