Restraints on freedom of expression can operate in two ways: most impose penalties after the event where the acceptable boundaries of free expression have been breached, but in rare instances prior restraint may be applied to prevent the expression in question. There is no criminal process by which a court can order prior restraint, unless publication would prejudice the administration of justice, but an injunction may be granted in civil proceedings brought by the Attorney-General (on his own account of by a relator action), by a local authority, or by an individual threatened with special damage.
Bonnard v Perryman  2 Ch 269, CA
A financial firm PP sued a newspaper DD for libellous assertions that PP had been trading dishonestly, and sought an interim injunction to restrain further publication pending trial. The judge granted such an order, but DD's appeal was allowed and the interim injunction was lifted. A six-man Court of Appeal said a judge does have power to impose prior restraint, but the power is discretionary and should be exercised only in the clearest cases. An interim injunction should not be granted where (as here) the defendant swears he can and will justify his assertions, unless the court is satisfied that he has no chance of success.
Holley v Smyth  1 All ER 853, Times 20/12/97, CA
D was the sole beneficiary of a trust and believed he had been defrauded by PP. He threatened to issue press releases making these allegations public unless PP made good D's alleged loss. PP were granted an interlocutory injunction restraining D from any such publication, but this was lifted on appeal. Auld LJ said the rule in Bonnard v Perryman is clearly that free speech is not to be subjected to prior restraint save in exceptional circumstances. There were no such circumstances here, and D had at least an arguable claim of justification.
Section 12 of the Human Rights Act 1998 should make prior restraint very rare. It prohibits the granting of any relief limiting freedom of expression unless the respondent is present or represented in court, or the applicant has taken all practicable steps to notify him, or there are (unspecified) compelling reasons for not notifying him, and goes on to prohibit any restraint of publication before trial unless the court thinks the applicant is likely to win on the substantive action. Freedom of expression is not expressly elevated above other rights such as the right to privacy - that would be inconsistent with the balancing exercise required by the European Convention - but the court is required to "have particular regard to" its importance.
In the rest of this section we consider some of the "restrictions prescribed by law".