It seems unreasonable that a person becomes an adult at the age of 18, but is then denied rights of adults until the age of 21.
If you are old enough to buy a gun, join the army, have a baby, buy a house with a 30 year mortgage, drive a car, vote, and be executed for a crime, you should also be able to buy a beer if you want to.
In my opinion holding back certain rights until 21 causes Americans to take longer maturing. This is not a good thing.
Also because of the hassle of obtaining alcohol, many teens instead abuse prescription and illegal drugs. When they can get hold of alcohol they tend to get the strongest thing they can find and binge drink on it.
It just doesn't make sense to run the law this way.
So no, the law in Britain needs to be left alone. If you are an adult you are an adult, it's that simple. Why copy America on this issue, when their system doesn't really work?