Van Duyn v Home Office
The British government denied Yvonne Van Duyn, a Dutch national, an entry permit because she was affiliated with Scientology, which the government had believed to be socially harmful. She sued, citing the Treaty of Rome and Community law, and the case was referred to the European Court of Justice.
Under Article 48 of the ECC Treaty, the Court ruled that states could exclude a national from another state on public policy grounds based only on the personal conduct of that individual, and in Van Duyn's case her affiliation with a group could be considered personal conduct. Thus, because Britain had in the seventies a public policy of preventing the spread of Scientology (this policy was repealed in 1980 after parliamentary review), the Home secretary's exclusion order of Van Duyn was allowed under community law.
However, Van Duyn must now be read in light of the more restrictive approach advanced in R v Bouchereau - activities must be socially harmful. (pg 553 Steiner and Woods)