Thousands of prisoners will seek legal advice after the Supreme Court ruled that trial judges had been wrongly interpreting a law relating to joint criminal enterprise for 30 years, lawyers predict.
But solicitors say it is impossible to know how many cases might reach the Court of Appeal or how many convictions might be overturned.
A panel of Supreme Court justices said on Thursday that prosecutors, judges and jurors had to take a different approach when dealing with defendants accused of being involved in some kinds of joint criminal enterprises.
Justices said the interpretation of part of the law relating to joint enterprise - which can result in people being convicted of assault or murder even if they did not strike the blow - had taken a "new turn" in the mid-1980s.
Senior judges had decided in 1984 that a "secondary party" would be guilty of murder if he or she "foresaw" the possibility that the "principal" might act with intent to cause death or serious harm
The Supreme Court said that development was wrong.
Justices said it was not right that someone should be guilty merely because they foresaw that a co-accused might commit a crime.
They said jurors should view "foresight" only as evidence to be taken into account, not as proof.
Five Supreme Court justices had analysed the issue at a hearing in London when considering an appeal by a man who was convicted of murder after egging on a friend to stab a solicitor.
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 - a former policeman - 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 allowed Jogee's appeal against conviction.
Justices said he would stay in prison pending a decision on whether he should be re-tried for murder or re-sentenced on the basis that he was guilty of manslaughter.
Mr Fyfe's widow, Tracey, 53, from Melton Mowbray, Leicestershire, said the ruling had left her "absolutely gutted".
She said she wanted Jogee re-tried on a murder charge.