MPs have called for ‘immediate steps’ to reform the ‘complex’ and ‘confusing’ law on joint enterprise.

The cross party Justice Committee says the doctrine is being applied ‘inconsistently’ and that legislation is needed to ensure justice for victims and defendants and to cut the high number of cases reaching the Court of Appeal.

A report, published today, says the lack of clarity over the common law doctrine is ‘unacceptable’ and recommends that the Ministry of Justice take ‘immediate steps’ to enshrine it in statute.

It recommends that the Director of Public Prosecutions issue urgent guidance on the use of joint enterprise when charging decisions are made, in particular on the relationship between association and complicity in gang-related violence and homicide. It also urges the DPP to collate data on the number of people charged under the joint enterprise doctrine every year and on the outcomes of cases.

Sir Alan Beith, the committee’s chair, said: ‘This area of law is vital to ensuring the prosecution and conviction of criminals involved in gang-related violence in particular, but is now so complex that juries may find it impossible to understand how to reach the right verdict.’

Joint enterprise is a form of secondary liability whereby a person who agrees to commit a crime with another becomes liable for all criminal acts committed by the principal person in the course of their joint criminal venture.

The common law doctrine has been developed by the courts over the years to ensure that all participants in a criminal enterprise could be held accountable.

The report says the committee would welcome evidence that the deterrent effect intended by the use of the doctrine discourages young people, who may be on the periphery of gang-related activity, from becoming involved in criminality. But it warned that over-charging under joint enterprise may deter potential witnesses who fear that they may be charged under the rule if they come forward.

Beith said: ‘The law on joint enterprise has a role in deterring young people from becoming involved in gangs but confusion over the law and how it works can put vital witnesses in fear of coming forward, allowing the real criminals to escape justice.’

He added: ‘It is also important to ensure that young people are not unnecessarily brought into the criminal justice system when they are on the edge of gang-related activity.’

The report follows the committee’s enquiry into the doctrine, announced in October 2011, prompted by concerns among campaigning groups that its operation had led to miscarriages of justice.

The Director of Public Prosecutions responded to the report with a promise of new guidance. Keir Starmer QC said: ‘I have decided that the Crown Prosecution Service will now produce guidance on the approach we will take to cases of joint enterprise, including guidance on the proper threshold at which association potentially becomes evidence of criminality.

‘This exercise will be done through consultation, with interested parties, on draft guidance in due course, and as with all CPS guidance it will be kept under review.’

He said the CPS would consult on the best way to collate statistics on cases involving joint enterprise.