³ÉÈË¿ìÊÖ

The decision that Junior Bayode will not face a retrial for a schoolboy's murder at London's Victoria Station marks the end of a case which saw an unprecedented use of a law called joint enterprise.

Some 20 teenagers originally faced murder charges following the 2010 murder of Sofyen Belamouadden under a law increasingly being used to tackle gang violence.

After four trials lasting 21 months, three have been convicted of murder, five of manslaughter, including Bayode, 12 of lesser charges and three cleared.

The case is the latest example of how the law of joint enterprise can be deployed to successfully prosecute crimes involving large numbers of people.

But some campaigners argue the law is a "lazy" option for prosecutors and can lead to miscarriages of justice.

The centuries-old law allows a whole group of people to be prosecuted for the differing roles they played in a murder. There is a version of the law in Scotland, although it is applied slightly differently.

Historically, joint enterprise helped authorities deal with duels, enabling them to prosecute the duellers, their supporters and doctors who treated the wounded.

To make a normal murder charge stick, prosecutors need to prove the defendant intended to kill.

But the terms of joint enterprise are different - and at the heart of it is the concept of foresight.

Prosecutors must prove the defendants were involved in some kind of common criminal enterprise and, in the course of their actions, the individuals could have foreseen that one member of the group might kill or inflict serious harm.

In other words, if three friends were walking down the road and one stabbed a passer-by, the others could not be prosecuted if they genuinely had no idea that their companion was carrying a knife or intended to use it.

But if the trio looked for trouble, and each person knew that one of them was carrying a knife as a weapon, then each could be convicted over its use because they could have foreseen the consequences.

The most well-known and controversial conviction involving joint enterprise was that of Derek Bentley in 1952, for the murder of a policeman.

He was convicted of the shooting and subsequently hanged. But he did not pull the trigger and the killer was too young to be sentenced to death.

Bentley was in fact convicted on his disputed words - "Let him have it" - and on the joint enterprise principle that he could have foreseen the outcome. After a long campaign, the .

A more recent case went all the way to the House of Lords.

In 2004, Tyrone Clarke was stabbed to death in a gang fight in Leeds - and four men were convicted of his murder. They lost their appeal after even though there was no evidence that any of the four had inflicted the fatal injuries.

The legislation has been used increasingly in recent years to deal with knife crime among teenage gangs as it allows police to cast a net widely and deal with walls of silence.

Metropolitan Police Commander Simon Foy said this was a reflection of detectives' growing experience in investigating such murders.

"I've heard it called a lazy law and that we're just scooping people up, but it's a painstaking account of everyone who has been involved. That description is not accurate," he says.

But campaign group Joint Enterprise Not Guilty by Association (Jengba) says the law promotes miscarriages of justice. It has been approached by 338 people who say they have been wrongfully convicted.

"Many of whom are serving life sentences for something they did not do, did not foresee what was going to happen nor intend to happen, but have been convicted by an archaic law that is being abused to get convictions and not justice," co-ordinator Gloria Morrison says.

You can find out more about the history and development of the law of joint enterprise by listening to this ³ÉÈË¿ìÊÖ Radio 4 Law in Action programme from 2009.