In the UK, copyright is supposedly limited by Article 10 of the European Convention on Human Rights. The analogous provision in the US is the First Amendment. In both jurisdictions, former political leaders have had their memoirs purloined and sued when someone else published extracts. President Ford and Lord Ashdown both won, but in the course of their victories the courts conceded that copyright must be limited by freedom of expression. It's my belief that both the Ashdown and Harper Row cases actuallly served to undermine the limitations on copyright.
The US Supreme Court in Harper Row held that the effect on the potential market for a work was "undoubtedly the single most important element of fair use" (the US copyright statute gives great weight to four matters which the courts should consider when determining if a use was fair). This is in effect largely an acceptance of the market failure theory of fair use which Wendy Gordon was propounding around the time the case was handed down. It implies that fair use might grow or recede as the ability of the rightholder to capture the value of the work changes. In a world where DRM may permit price-discriminating rightholders to capture much more of the value of a work there is likely to be a qualitative diminution in the scope of fair use. To protect fair use from becoming coextensive with that proportion of the value of a work which can never be economically exploited might be achieved by a reformulation of the fair use rule along the lines of the commercial competitive conduct of the unfair user as opposed to the resultant cumulative market impact of his (and others') use.
In the UK case, Ashdown v Sunday Telegraph, the Court considered the interaction between copyright and the right to freedom of expression as formulated in Article 10 of ECHR. The Article incorporates a three-part test: abridgement of the right may only be done if prescribed by law, if necessary in a democratic society, and if for the protection of the rights of others.
The Court rejected without consideration the view put forth by Boukema in the 1960s that the rights against which Article 10 is ineffective ("the rights of others") only refers to other rights set forth in the Convention, as opposed to other interests covered by the Protocols or outside the ECHR system altogether, and opted for a more arbitrary and fluid standard of so-called fundamental rights liable to permit restrictions on freedom of expression wherever this is in the public interest, the opposite of what many have mistaken the ECHR provisions to mean. Into the first Protocol to the Convention, which concerns itself with private property rights in "possessions", the Court read a protection of a much broader conception of private property interests in general. Arguably the reading was more general than the word "possessions" can reasonably be held to cover, as it was extended to interests in intangibles such as copyright.
The third part of the test having been circumvented, the second part, relating to democratic necessity, is practically ignored; the treatment seems to revolve around whether or not ECHR would need to be considered in relation to the facts of every IPR case (which argument I admit to not understanding), and the number of statutory exceptions to copyright. It is concluded on the basis merely of the existence of statutory exceptions to a right that the right does not infringe some other right more than is necessary in a democratic society (though the Court of Appeals did employ a comparative law justification in support of this). This all begs the question of how much the copyright statute could be tightened up before it infringed ECHR.
So in the US, fair use is made to lean most heavily on that one of its four pillars most susceptible to the ground moving beneath it. The situation in the UK appears to be that, to the extent that Ashdown was rightly decided at all, copyright is unaffected by freedom of expression so long as it has at least some exceptions. Both seem to permit copyright to expand almost to the total exclusion of fair use.