The press testing the boundaries of reporting in criminal cases could undermine the jury system, the attorney general has warned.

In a speech at City University on contempt and balancing the freedom of the press with the fair administration of justice, Dominic Grieve QC said he had become increasingly concerned at what he perceived to be ‘the increasing tendency of the press to test the boundaries of what was acceptable over the reporting of criminal cases’.

He said: ‘At times it appeared to me the press had lost any sense of internal constraint and felt able, indeed entitled, to print what they wished, shielded by the right of freedom of expression without any of the concomitant responsibilities.’

Grieve said the creation of the ‘bad character provision’ in the Criminal Justice Act 2003, which allows a defendant's previous convictions to be admitted in evidence, may have exacerbated the problem. ‘The potential to admit evidence of a defendant's previous convictions has led some in the press to believe they can print, without let or hindrance, all manner of true facts, abuse and nonsense,’ he said.

But, he said, the admission of evidence was subject to rules and judicial oversight, and it was not for the press to ‘usurp the role of the judge’ or use the admission of bad character evidence as ‘an excuse to throw responsible reporting to the wind’.

Grieve said: ‘I was concerned that, uncontrolled, such reporting could eventually undermine the jury system. Jurors must reach a verdict solely on the basis of the evidence presented to them in court.’

He said the freedom of expression enshrined in Article 10 of the European Convention came with duties and responsibilities, and he urged the press to act responsibly, with ‘humanity’ and observing ‘common decency’.

‘If society is to function, if we are to avoid anarchy, all of us who enjoy this right must recognise the need to show, at times, restraint not to say humanity. If a free press is at the heart of democratic society, it is essential it should act responsibly,’ he said.

Grieve cited three cases over the last year where the courts had found a contempt of court.

The first case involved the internet and online publication of a picture of a defendant in a murder trial holding a pistol; the second concerned the press’s coverage of the arrest of Christopher Jefferies; and the third involved a juror contacting a defendant on Facebook.

He said the ‘revolution in methods of communication’ would increase the power and the role of the internet in reporting of the courts, but warned that the internet did not put users above the law or provide immunity from prosecution. ‘Unlike major news organisations, which on the whole act in a responsible and measured manner, the inhabitants of the internet often feel themselves to be unconstrained by the laws of the land.

‘There is a certain belief that so long as something is published in cyberspace there is no need to respect the laws of contempt or libel. This is mistaken,’ he said.

Grieve added: ‘While I accept the danger posed to the administration of justice by many bloggers is minimal, we should not underestimate the potential for a blog or tweet to go viral.’

He warned: ‘An online article that breaches the strict liability rule runs the risk of running afoul of the law of contempt.’ But he said he did not seek confrontation and had ‘no desire to act as a policeman’ and that he would try to preserve the rights of free press that acted professionally and ethically.