Oh, I do know it's a good thing in a way but I hate it still! 
My sister went in to M&S last summer with her two children, who were 6 and 4 at the time to buy some food and one of those little bottles of wine to give to her daughters teacher and she was ID'd then! What underage teenager goes to M&S with two children to buy a small bottle of wine with £50 worth of food if they're trying their luck?! BTW, she was 35 at the time...
So it must run in the family!