European Convention for Human Rights

Article 10 - Freedom of expression

1 Everyone has the right to freedom of expression. This right shall include
freedom to hold opinions and to receive and impart information and ideas
without interference by public authority and regardless of frontiers. This
article shall not prevent States from requiring the licensing of
broadcasting, television or cinema enterprises.

2 The exercise of these freedoms, since it carries with it duties and
responsibilities, may be subject to such formalities, conditions,
restrictions or penalties as are prescribed by law and are necessary in a
democratic society, in the interests of national security, territorial
integrity or public safety, for the prevention of disorder or crime, for the
protection of health or morals, for the protection of the reputation or
rights of others, for preventing the disclosure of information received in
confidence, or for maintaining the authority and impartiality of the
judiciary.

Essence

Firstly, note that this provision covers both the freedom of
expression ("send") and the freedom to gather information ("receive").
Subsection 2 enumerates the allowed restrictions. Perhaps Internet filtering
falls under one of the exceptions? I don't know what the European Courts of
Human Rights has said about this. But usually it interprets the restrictions
restrictively.