Mr Justice Saunders expressed his “concern” at David Cameron’s public apology for hiring Coulson in 2007, which was issued after he was found guilty of plotting to hack phones at the News of the World.
On Tuesday, Cameron led the way in what the judge described as “open season” on political reaction which saw Chancellor of the Exchequer George Osborne, Labour leader Ed Miliband and others follow suit.
At the time, the jury was still deliberating on two remaining counts against Coulson, 46, of allegedly conspiring with former royal editor Clive Goodman, 56, to commit misconduct in a public office in relation to paying police officers for two royal phone directories.
Yesterday the judge refused a bid by Coulson’s legal team to excuse the jury from deciding on the outstanding charges after considering the argument the ex tabloid editor could no longer received a fair trial amid such a “maelstrom of reporting”.
An hour later, jurors concluded they could not agree and were discharged after nine days’ deliberation and 139 days of the trial.
Coulson now faces up to two years in prison when he is sentenced next week along with others who have already pleaded guilty.
Yesterday, the judge said he had asked the prime minister for an explanation and was told by his principal private secretary: “The prime minister was responding to the guilty verdict on hacking charges that had been delivered in open court.”
But Mr Justice Saunders said the prime minister had “missed the point” and revealed information the jury had not been told during the trial for legal reasons.
“My sole concern is to ensure that justice is done. Politicians have other imperatives and I understand that. Whether the political imperative was such that statements could not await all the verdicts, I leave to others to judge.
“The press in court have been extremely responsible in their reporting of this case but when politicians regard it as open season, one cannot expect the press to remain silent. I accept that this case is very unusual if not unique, but the situation could occur again and I would urge that discussions take place to try and set up a better system of dealing with it.”
Coulson’s lawyer Timothy Langdale had earlier blamed the politicians for putting politics before justice.
“This was an extraordinary situation where the ill advised and premature intervention by the prime minister and others to avoid political damage or make political capital is almost impossible for the jury to ignore. It strikes at the heart of justice. It is astonishing, we say unprecedented, for a prime minister to make public comments at such a crucial juncture in trial proceedings.”
But Andrew Edis, prosecuting, argued: “What Mr Cameron said is Mr Coulson told him a lie. What Mr Miliband said is Mr Coulson is a criminal. The jury were satisfied so they were sure Mr Coulson was guilty of count one which makes him to that extent a criminal. In coming to that conclusion they decided he had told them lies for days on end about phone hacking so Mr Cameron was not really telling them anything that they did not know.”
Cameron was “unwise” to have spoken out, cabinet veteran Kenneth Clarke has said. Clarke, a qualified barrister, said Cameron had appeared not to have considered the legal implications when he made his remarks.
“It was unwise. They should have taken some legal advice first but I doubt whether it ever crossed David’s mind,” he told BBC Radio 4’s The World at One.