Deputy Prime Minister Nick Clegg has said the law needs to be changed to give journalists accused of corrupting public officials by paying for stories a clear public interest defence.
The offence of misconduct in a public office dates back the 13th century. Its use against journalist has been thrown into question by a decision on Friday to quash the conviction of a News of the World journalist tried for conspiracy to commit this crime.
The Liberal Democrat leader criticised the "opaque" nature of the current system and said prosecutors were relying on outdated laws in deciding whether journalists should go on trial.
Clegg, speaking as he launched the Lib Dems' election campaign in thmarginal Oxford West and Abingdon seat, said: "I have long been concerned that the laws of the land are not clear enough on the public interest defence for journalists and other people who are covering information in the interests of the public…
"It's just far too opaque, in too many of our laws, exactly what is the strength and nature of a public interest defence.
"I would like to see that clarified in law, my party has always advocated that. The fact that prosecutors are relying on 13th century laws, that we don't have an up-to-date definition of what a public interest defence is, shows the need for a proper review and a proper reform of the law in this area."
His comments follow the quashing of the conviction of the first journalist to be found guilty of paying a public official in the wake of the high-profile Operation Elveden probe.
The former News of the World reporter was handed a six-month suspended sentence after being found guilty of paying a prison officer for information at the Old Bailey last November.
In turn, the officer was jailed for three-and-a-half years for misconduct in a public office while his friend was given 30 weeks behind bars.
All three, who cannot be named for legal reasons, launched an appeal and the Lord Chief Justice ruled that their convictions should be quashed.
He found the trial judge Charles Wide had "misdirected" the jury on a key aspect of the ancient common law offence of misconduct in a public office in relation to the "level of seriousness" required.
Under the offence, which can be traced back to the 13th century, the misconduct had to be "to such a degree as to amount to an abuse of the public's trust in the office holder".