Johnathan Marcus of the BBC has written a good summary of some of the issues surrounding NATO's BMD programme. You can read it here. It contains a great quote from Professor Ted Postol about the lack of missile threat to Europe:
However, a leading expert on missile defence technology, Professor Theodore Postol of the Massachusetts Institute of Technology, believes that this potential threat has been much overstated.
"The fundamental long-term threat from Iran is from nuclear weapons. But for now Iran does not have the bomb. A ballistic missile without a nuclear weapon," he says, "is like a terrorist bomber without an explosive vest."