If you live in England and you have been baptized, you can now un-baptize yourself.
Given that children are baptized against their will and made to be Xian (this isn't limited to Xianity either) this is something that is long overdue. OTOH, you don't really need a certificate to reject religion. In some countries, however, it appears that you really should make it known to the church. As the article points out:
According to Argentine campaigner Ariel Bellino, a former Catholic: "The church counts all those who've been baptized as Catholic and lobbies for legislation based on that number, so we're trying to convey the importance of people expressing they no longer belong to the church." Campaigners say that's particularly important in Argentina, where liberal social values frequently clash with Roman Catholic doctrine related to issues such as birth control, abstinence before marriage and homosexuality; in 2003, Buenos Aries became the first city in South America to legalize gay civil unions.
Back in Britain, Michael Evans, an atheist and former journalist who downloaded the de-baptism certificate in March, believes the Church of England claims more members than it actually has in order to shore up its influence in the secular world. "It claims to speak for the majority of people in Britain," he says.
In countries where this practice happens, it is important to make your rejection of religion known so that the church can not use your name as a number to gain influence that it does not deserve. (Let's be frank here, churches don't deserve any political influence, nor should they have any by default.)