English law is common law. For further reading I recommend the following two Wikipedia links: http://en.wikipedia.org/wiki/Conspiracy_(crime) http://en.wikipedia.org/wiki/Accessory_(legal_term)

It seems that at least in the United States there's quite a broad range of things that courts consider as "conspiracy". For example, a few years ago Reinhard Berkau (a German lawyer) was sentenced to prison in the US, because of a crime one of his clients did. He also published a book on his experiences (unfortunately in German only) in case you're interested in the background.