Hi Juan
It may not be the law that dictates window blind setting for take off and landing but it most definitely is a VS requirement to have blinds up for t/o and landing.
As previously mentioned the reason is for the crew to easily have a full view of what is going on outside the aircraft with one glance, 'in the unlikely event' as well as a means for your eyes to adjust to outside daylight conditions. The very same reason cabin lights are dimmed for t/o or landing in the hours of darkness.
Whilst it is not necessarily the law, it is the airline's safety requirement and therefore to refuse would go against the Air Navigation Order. The Captain has the final say on board any aircraft and if the blind setting is within the airline's procedures then he would request all blinds up for t/o and landing without a doubt.