UK law on contempt applies to any publication that creates 'a substantial risk' of prejudicing the course of justice

Although not covered by UK contempt laws, the disappearance of Madeleine McCann demonstrates the consequences of overreporting criminal cases. The Express Newspaper Group had to publish front-page apologies to the McCanns for false allegations. Photograph: Cate Gillon/Getty Images

UK law on contempt is set out in the 1981 Contempt of Court Act, which applies to all publications that create "a substantial risk" the course of justice will be "seriously prejudiced". The 1981 Act was passed, in part, in response to the decision of the European Court of Human Rights in a case involving The Sunday Times, and was perceived as representing a shift in the balance of public interest in favour of freedom of speech.The law does not set out what is allowed or not but lays down broad principles: it is a question of judgment in each case as to what may create "substantial risk". The most obvious examples are revealing a defendant's previous convictions or otherwise implying guilt.

In the US, the power of the courts to punish for contempt by publication is extremely limited. Compare, for example, the UK position to the US media coverage of the proceedings against OJ Simpson, Michael Jackson and Phil Spector. Or that of Los Angeles Lakers basketball player Kobe Bryant, charged with the rape of a young woman in a hotel in Colorado. One cable television station invited viewers to vote on Bryant's innocence or guilt ' a US judge subsequently dismissed the case against Bryant, after the accused failed to testify. There is a TV channel and website dedicated to ongoing prosecutions, where you can watch the trial, access the evidence and vote on matters relating to the trial as a "13th" juror.

In practice, a number of matters are relevant when considering if a publication is likely to create a "substantial risk of serious prejudice": if the trial involves lay assessors, such as a jury (judges should be able to rise above what they read in the papers); the likelihood of the publication coming to a potential juror's attention; its likely impact on an ordinary reader at the time of publication; and the so-called fade factor (how far away the trial is likely to be) ' the longer the gap between publication and the trial, the less the substantial risk of serious prejudice is likely to be. In previous cases involving the media, gaps of three and 10 months between publication and trial were held to have lessened any risk; in another case involving ITN and the publication of widely circulated information that a prisoner who had escaped from jail was a convicted IRA terrorist did not negate that risk.

Publication during a trial is clearly problematic. In June 1999 the Sun published serious allegations about a defendant in a murder trial just as the jury were retiring; the charge was dropped and the Sun was fined '35,000. The collapse of an assault trial involving Leeds United footballers in April 2001, following publication of an interview with the victim's father in the Sunday Mirror (which some jury members had read while deliberating), resulted in its editor, Colin Myler, resigning; the paper was subsequently found guilty of contempt of court, fined '75,000 and ordered to pay costs of '100,000.

In recent years the UK attorney general's office has taken to issuing what it calls "guidance" in high-profile criminal cases (as it has done in the Joanna Yeates case) but this does no more than remind newspaper lawyers what they already know. Whether because successive attorney generals have believed the law is against them or because they think that coverage had been distastefulbut not overstepped the line, there has been an apparent reluctance to bring contempt proceeding against the media in recent years over their post-arrest/pre-trial reporting. Judges seem to accept that most pre-trial coverage, while it may be prejudicial, falls short of creating a "substantial risk of being seriously prejudicial". On a practical level, one factor that will rein in the media's reporting of a case is the risk of being sued for defamation. Go too far in reporting speculation and innuendo after an arrest and there is a real risk of that if the accused is not charged.

Although Madeleine McCann's disappearance took place abroad and was not covered by UK contempt rules, it serves as a salutory reminder of the consequences for the UK media of overreporting criminal cases. Following accusations in the press, Gerry and Kate McCann and Robert Murat instigated libel actions: the Daily Express and the Daily Star published front-page apologies and agreed to pay the McCanns '550,000 in damages; and a group of British newspapers settled with Murat for a '600,000 payout and issued a public apology. The Tapas Seven (friends of the McCanns) were awarded about '375,000 in damages and secured printed apologies from Express Newspapers.

Things have changed greatly since 1981, not least with the advent of new technology and the web, which have made reporting a truly global affair, reaching into the corners of every country in the world. Looking forward, the options appear to be: enforce the present regime more rigorously, based on the belief that jurors are easily influenced and misled and consequently need to be protected; reinstate the practice of isolating juries by sending them to hotels to deliberate their verdicts ' this is unlikely to happen other than in the most sensitive of cases, as it is too expensive; or operate tighter jury vetting to see if people have been influenced.

Realistically, the UK courts are fighting a losing battle in trying to control publications under the contempt of court provisions ' even if the law in the UK were to be made more restrictive, it would not restrict foreign media outlets or the blogosphere.

The sensible way forward appears to be to give jurors robust instructions at the outset of a trial ' not to discuss the case with others; to disregard any media reports; not to be tempted to be amateur detectives and go searching on the internet; to make their decision based only on the evidence they hear in court.

In 1996, the then lord chief justice, Peter Taylor, refused to accept as a ground of appeal against conviction by Rosemary West (who had been sentenced to life imprisonment for the murder of 10 young women and girls) that adverse publicity surrounding her arrest had affected the jury's ability to reach a fair verdict; he felt juries were capable of concentrating on the evidence and resisting the media's sensationalist excesses.

Gill Phillips is the Guardian's director of editorial legal services