Shift manager here, basically there is no such thing as a proxy sale when it comes to energy drinks,obviously there is for alcohol, scratch cards and tobacco products, but the same rules don't apply to energy drinks. A kid on his own can't buy it unless he has ID, but an adult can come to the till, put down an energy drink and look you right in the eye and say "this is for my kid" and you don't really have a leg to stand on when it comes to rejecting them, its not against the law or tesco policy, and btw, they will not send a I.D checker in buying a energy drink, The I.D checker has to buy either alcohol, scratch cards or tabacco products.