Can we afford to prosecute people any more? We have already seen the government’s proposals to introduce what it calls ‘deferred’ prosecution agreements, under which companies that commit economic crimes will be able to escape criminal charges, indefinitely, if they agree to pay penalties and comply with other conditions. Last week, we were introduced to a new draft code for crown prosecutors, which says the cost of a prosecution should be one of the factors to be considered in deciding whether it should go ahead.

The new code, open for consultation until 10 October, will be the seventh to be issued since the Crown Prosecution Service was set up in 1986. Like previous versions, it tells prosecutors they must be sure there is a ‘realistic prospect of conviction’ before deciding whether a prosecution would be in the public interest.

Efforts have been made to use plain English in the latest edition, either because the CPS wants its code to be understood by the wider public or because prosecutors can no longer be assumed to have the language skills they had 25 years ago. Then, prosecutors were told that ‘multiplicity of charging should never be used in order to obtain leverage for the offering of a plea of guilty’. Now, the code says that ‘prosecutors should never go ahead with more charges than are necessary just to encourage a defendant to plead guilty to a few’. A venerated quotation from Sir Hartley Shawcross in 1951 has also finally gone.

But there is still scope for greater clarity, for example by substituting ‘decide’ in phrases such as ‘the custody officer must determine…’ And there have been some late amendments to the draft code in far-from-plain English - such as ‘it is essential that regard is also given to the public interest factors identified when considering the other questions in paragraph 4.14(a) to (g)’.

What has rung alarm bells, though, is the section headed ‘proportionality’. In telling prosecutors to consider whether a prosecution is ‘proportionate to the likely outcome’, it asks them to take account of the cost to the prosecution service and the wider criminal justice system of bringing a case to court, ‘especially where it could be regarded as excessive when weighed against any likely penalty’.

All very pragmatic, but not particularly new. Keir Starmer, who heads the CPS as director of public prosecutions, stressed that proportionality had been included in the first two editions of the code. Although the term itself was not current in 1986, he was right to point out the first edition advised prosecutors to ‘weigh the likely penalty with the likely length and cost of the proceedings’ in deciding whether to seek a Crown court trial ‘when the circumstances of an offence are not particularly serious’.

The new draft does seem to give more emphasis to the option of ‘offering the offender the opportunity to have the matter dealt with by an out-of-court disposal’. But this wording is included in the current edition and there was a similar reference to a ‘disposal less than prosecution, for example, a caution’ in the 1986 code. Writing about that edition for a book on the CPS published 25 years ago, I referred to ‘this cost-conscious age’. We are rightly more conscious of costs now but, even in 1987, we did not ignore them.

Where the new draft is much less useful than its predecessor is advising prosecutors whether the available evidence is admissible, reliable and credible. Indeed, ‘reliable’ and ‘credible’ are such similar tests of evidence that the sixth edition of the code defined one in terms of the other.

Detailed guidance on the tests to be applied is all the more necessary now that judges are going to such lengths to protect juries from information that would otherwise be in the public domain. Simon Harwood was acquitted of manslaughter last week after Mr Justice Fulford asked two newspapers to remove online accounts of the police officer’s disciplinary record from published reports. Also last week, Mr Justice Flaux ordered the BBC not to broadcast two drama-documentaries about the London riots in 2011. That was because a jury was about to consider whether eight men had murdered three friends who had been hit by a car during riots last summer in Birmingham.

Because all eight defendants were acquitted, as was Harwood, we can infer that neither jury was improperly influenced: these temporary restrictions on freedom of expression achieved their intended aims. But both judges will have had to consider whether their attempts to protect jurors from potentially prejudicial material were at risk of being thwarted by Twitter or other online social networking services.

Modern technology makes it increasingly difficult to ensure that jurors are not exposed to evidence they are not meant to see - although, ironically, it was two traditional newspapers that were found to have been in contempt of court last week. After Levi Bellfield had been convicted of kidnapping and murdering Milly Dowler, the Daily Mail and Daily Mirror published evidence that was prejudicial to the remaining charge he faced, of attempting to kidnap Rachel Cowles.

If Twitter and even the mainstream media can no longer be controlled, we have to ask whether it is time to trust juries a little more and worry about what they hear outside court a little less. Either that, or we will have to bring fewer prosecutions in high-profile cases. Whatever happens, it cannot be very long before we need yet another edition of the code for Crown prosecutors.