The family of a man shot dead by police while naked and unarmed are to put the force on trial for unlawful killing.
James Ashley was in bed when officers opened fire in 1998
Appeal judges ruled that there should be a civil trial over whether Pc Chris Sherwood was guilty of assault and battery when he shot James Ashley.
Sussex Police must now show that Pc Sherwood, who was acquitted of murder in a criminal trial, acted in self defence during a raid in East Sussex.
James Ashley, 39, from Liverpool, was shot dead in Hastings in 1998.
The judgement was delivered by the Court of Appeal's Master of the Rolls, Sir Anthony Clarke, on Thursday.
He said the Ashley family should be allowed to take the battery issue to court "if only in order to seek a declaration that the deceased was unlawfully killed by Pc Sherwood, especially in circumstances in which there has been no inquest or public inquiry into the death".
Sir Anthony also allowed allegations of wrongful conduct in office by the chief constable of Sussex to go to trial.
Edward Faulks QC, who represented the police during the hearing, told the judges: "The self defence issue is a point of great constitutional importance.
"The effect of this court's order is that there will be a murder trial which could result in a declaration of unlawful killing."
Speaking after the ruling, James Ashley's son, also called James, said: "Nothing will ever bring my dad back, but I am very pleased with the outcome of this appeal.
"Maybe our family will now get some answers."
The victim's father, also called James, said: "I am happy that a court has reached a positive decision after eight years."
James Ashley was killed during a raid on his flat in St Leonards in the early hours of January 1998. He was shot in the back.
Sussex police suspected Mr Ashley of dealing drugs and had a warrant to search the flat.
His father and son are bringing civil claims of assault and battery, false imprisonment and negligence that arise out of the shooting.
They are also claiming misfeasance and negligence on the part of police after the shooting.
Misfeasant conduct is when a public officer intends to damage someone or recklessly acts unlawfully in a way that might injure someone.
Among the family's allegations of misfeasance are that the officers involved deliberately released incorrect information to the media, obstructed an independent investigation and fabricated evidence.
Sir Anthony told the court that the chief constable has already admitted negligence in the shooting claim.
The amount of compensation for the family will be set at the same time as the trial over assault and battery.
Addressing the battery claim, Sir Anthony said: "On the facts here, it is true that Pc Sherwood was acquitted of murder on the direction of the trial judge."
But he said the burden of proof in the criminal trial was on the prosecution, while in civil trial it rests with the defendant.
"There is, to my mind, a public interest in allowing this aspect of the claim against the police to proceed," he added.