A senior judge expressed deep sorrow for the family of Pc Andrew Harper as he halted the trial of his alleged killers over the coronavirus pandemic.
Mr Justice Edis announced the decision to discharge the jury and adjourn the Old Bailey trial with a “heavy heart” after three jurors went into self-isolation.
Last week, he had resisted calls by defence barristers to stop the trial after being forced to discharge two jurors, leaving just 10 to carry on.
On Monday, he discharged the entire panel on hearing a third juror had gone into self-isolation over the weekend due to their elderly father becoming ill.
In a statement, the judge said: “I have taken this decision with a heavy heart because I am acutely conscious of the need of those who loved Police Constable Harper (who would have been 29 yesterday) for this process to come to a conclusion.
“I am deeply sorry for them. I know also that the colleagues who dealt with the events of that terrible night and who have given evidence will also suffer additional distress because of what has happened.”
Mr Justice Edis acknowledged the decision meant a “significant delay” in the trial of the three teenage defendants, who remain in custody.
Praising the jury, he said: “I also wish to say that I am deeply grateful to the jury, all 12 of them. They showed a remarkable level of commitment to this trial as the crisis developed around us, and that involved courage as well as public spirit.
“They appreciated the essential nature of trials of this kind and put themselves at the service of the public to see it through, knowing the risk which that involved.”
Henry Long, 18, and two 17-year-old boys are accused of killing Pc Harper in August last year.
The 28-year-old Thames Valley officer became entangled in a tow rope as he tried to apprehend quad bike thieves, jurors were told.
The stricken officer was probably knocked unconscious as he fell, then dragged more than a mile along country lanes behind a Seat Toledo car driven by Long, the court was told.
Colleagues desperately tried to save him but he had suffered catastrophic injuries and died at the scene near Sulhamstead, in Berkshire.
Long, of Mortimer, Reading, admitted manslaughter and conspiracy to steal a quad bike but denied murder.
The two youths, who cannot be named for legal reasons, admitted conspiracy to steal but denied murder and manslaughter.
Pc Harper’s widow Lissie and other family members had attended the trial which opened on March 10.
Over two weeks, the jury viewed harrowing dash-cam footage and heard a string of eyewitness accounts, with one describing how he at first mistook Pc Harper’s body for a deer.
Mr Justice Edis set a hearing on June 1 to review the situation and, if possible, set a date for the trial to start again.
He said in his statement that the case would take “priority” when trials resumed.
The trial had been one of eight at the Old Bailey to continue last week despite the pandemic.
More than a dozen high-profile Old Bailey trials had already been postponed following measures to delay the spread of Covid-19.
Last Tuesday, the Lord Chief Justice of England and Wales announced that upcoming criminal trials lasting more than three days would be put off.
On Monday, further measures were announced putting all criminal trials with juries on hold.
Reacting to the announcement in court, a Thames Valley Police spokesman said: “Clearly this is disappointing and will be a very difficult decision for Pc Harper’s family to hear.
“However, Thames Valley Police fully accepts and supports the judge’s decision and recognises the gravity of the ongoing national situation.”