The law on joint enterprise - which saw a Rainhill man convicted of murder - has been wrongly interpreted over the past 30 years, the Supreme Court has ruled.
Joint enterprise can result in people being convicted of assault or murder even if they did not strike the blow.
The judgment, delivered at a hearing in London on Thursday, could lead to people convicted of joint enterprise crimes launching appeals.
Gerard Childs and Stephen Price with sentenced to life imprisonment after being convicted under joint enterprise of the murder of Jonathan Fitchett, 22.
In July of last year, Childs and Price, both 28, had their conviction quashed as “unsafe”.
Childs was instead convicted of manslaughter and ordered to serve seven years and Price given three years for affray.
During his imprisonment for murder, Childs’s girlfriend, Toni Murphy, took part in demonstrations by the Joint Enterprise Not Guilty By Association (JENGBA) against joint enterprise.
The Supreme Court justices today said prosecutors, judges and jurors must take a different approach when dealing with such defendants.
They said it was not right that someone should be guilty merely because they foresaw that a co-accused might commit a crime.
Jurors should view “foresight” only as evidence to be taken into account, not as proof.
A panel of five Supreme Court justices analysed the issue of joint enterprise at a hearing in London in October when considering an appeal by a man who was convicted of murder after egging on a friend to stab a former policeman.
Ameen Jogee and Mohammed Hirsi, both in their 20s, were given life sentences at Nottingham Crown Court in March 2012 after being convicted of Paul Fyfe’s murder.
Jurors heard that Hirsi stabbed Mr Fyfe at a house in Leicester in June 2011 while being egged on by Jogee.
A judge imposed a minimum 22-year term on Hirsi, who lived in Leicester, and a minimum of 20 years on Jogee, who was of no fixed address.
Jogee’s minimum term was cut to 18 years by the Court of Appeal.
The Supreme Court has now allowed Jogee’s appeal against conviction but he will stay in prison while lawyers decide whether he should be retried.
Speaking before the ruling, Mr Fyfe’s widow said if Jogee’s appeal was upheld it could mean killers will “literally be getting away with murder”.
Tracey Fyfe said she regarded Jogee as culpable for her husband’s death because he knew what Hirsi was doing and was egging him on.
She said: “I think it is a very important law and it think it would be quite devastating for the victims’ families like us, which would mean that criminals like Ameen Jogee would literally be getting away with murder.”