By Martin Hickman.Two key prosecution witnesses against former News of the World editor Andy Coulson are "thoroughly tainted", his lawyer told the phone hacking trial today.Timothy Langdale, QC, attacked the credibility of ex-NoW reporters Clive Goodman and Dan Evans at the start of his two-day closing speech at the Old Bailey.In their evidence, both Mr Goodman, the royal editor, and Evans, a features reporter, claimed that Mr Coulson knew about their hacking.Mr Langdale told the jury: "Seldom have there been cases, you may think, where two star witnesses have been branded by the prosecution, after they have given their evidence, as so unreliable that you should only rely on their evidence if there is something independent to back it up."He said that the police and prosecuting authorities had failed to be rigorous, open and transparent while making their case against Mr Coulson and that mistakes uncovered during the trial demonstrated its weaknesses.In particular, he said Mr Evans, who claimed he played a tape of a hacked message to Mr Coulson in the News of the World's office, was "dishonest" and that his allegations had been disproved by the facts.Mr Coulson's diary showed that he was not at Wapping when Evans claimed he had been, and call data showed that Evans had not hacked actor Daniel Craig's phone when he said he had, the QC said.He branded Mr Goodman - who claimed that Mr Coulson had approved an operation to hack members of the Royal Household - as an "unreliable witness."Opening his closing speech, Mr Langdale compared the prosecution case against his client to be a "juggernaut" that kept going whatever obstacles were placed in its way, telling the jury: "But you do not have to be swept before it."Telling the jurors that they would have to rigorous, open-minded and fair when considering their verdicts, he added: "There must be no thought that someone high up in the organisation [News International] has to pay for phone hacking."He said: "It's not News International or the tabloid press, but only Andy Coulson [on trial]. Judge the evidence against him and nothing else."He said that if phone hacking had been so widely known about at the News of the World, as the prosecution contended, why were there no emails (bar the prosecution's claim that Mr Coulson's "Do his phone" comment in one was an instruction to hack) in which reporters or journalists requested or referred to hacks.And if hacking was so well known and Mr Coulson was a co-conspirator, why did he not take care to protect his own hacking - because he himself was a victim of Glenn Mulcaire's voicemail interceptions, Mr Langdale added.Mr Langdale is scheduled to finish his speech tomorrow afternoon. The judge is expected to do his summing up next week.