The success of the new system of press regulation will depend on how many newspapers sign up to it. Some of Britain's largest newspaper publishing groups say they are considering the deal, but may yet opt out.
UK Editor Lucy Manning reports:
David Cameron has insisted a cross-party agreement for a new system of press regulation protects the principle of the free press.
Labour says this is just the sort of legal under-pinning they were looking for but the Conservatives say that no such press law will exist.
Is there a chance tomorrow's Commons' votes on press regulation may not go ahead? Could there be agreement between the parties after all?