According to reports, the Advertising Standards Authority (ASA) has banned two WKD/Smirnoff adverts because they thought the adverts were "too childish" and may target youth drinkers. You can read the Advertising Standards Authority's report into the adverts at http://www.asa.org.uk.
Although I hate alcohol, I think banning the adverts altogether was a bit too harsh, as long as the adverts are shown after the watershed and during programmes children don't normally watch, I don't see the harm of the adverts. Plus, it should be up to the shop keepers not to sell alcohol to children as well.