The changes did not mean “a green light” to report such evidence and doing so could still be in breach of contempt laws, Lord Goldsmith, QC, the Attorney-General said.

“To those who take that view I would sound a strong note of caution,” he told a seminar in London. “There is to be no automatic admission of such evidence. It will be a matter for the judge at trial.

“It will not be possible for journalists to know at the point of arrest or in the period leading up to trial what rulings will be made,” he said.

Publication of previous convictions or other material relating to the accused’s supposed bad character could therefore give rise to a substantial risk of serious prejudice.”

Lord Goldsmith also highlighted the risk posed by online newspaper archives. Jurors were now free to surf the web and could come across articles written months before that could be prejudicial, he said. Articles on a website that were not prejudicial when written could constitute contempt at the time of trial and should be removed.

“If they are on the web, there is a real risk that they can be found by the jury. Of course, the judge can give direction to the jury not to surf the web but . . . that is not a very easy direction to give.

“The media therefore has to be aware of this risk and be prepared, where there is a substantial risk of serious prejudice to remove reports from websites, even when the report, when it first appeared in the printed press, did not give rise to a substantial risk, due to the fade factor (the time likely to elapse before trial).”

Lord Goldsmith also reminded the media that such a “fade factor” was not a guarantee that jurors would forget all details they had read. Unusual facts in simple cases could stick in the mind, he said.

Referring to the guidance he issues from time to time to editors, Lord Goldsmith said he did not believe this had “any inappropriate chilling effect on the media.”

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