The judge in George Galloway's High Court libel case against the Telegraph has retired to consider his verdict.
Mr Galloway has branded the story "outrageous"
The Glasgow Kelvin MP is suing the newspaper over claims he took £375,000 from Saddam Hussein's Iraqi regime.
Richard Rampton QC, told the High Court Mr Galloway was not given a "cat in Hell's chance" of defending himself against the allegations.
The newspaper said the documents on which the claims were based showed a "thundering case to answer".
It had not been the Daily Telegraph's intention to "suggest guilt", James Price QC told Justice Eady who heard the case in London without a jury.
The QC told the court: "I'm making no allegation about whether Mr Galloway is guilty or not but it is absolutely plain that there is a thundering case to answer here."
It had been in the public interest for it to publish the contents of documents its reporter, David Blair, said he found in the Iraqi foreign ministry in Baghdad, Mr Price added.
What had emerged was "one of the most important stories of a most important time".
Any criticism of the integrity and professionalism of the reporters involved was "entirely misplaced", he told the court.
Daily Telegraph executive editor Neil Darbyshire also told the court he was certain the documents used for the story were genuine and in the public interest.
Mr Galloway had been a vocal opponent of the war and the documents had seemed to suggest a greater degree of cooperation between the MP and the Iraqi regime than previously known, he argued.
"It might also have offered some insight into the motives for his well-known
pro-Saddam stance," he said.
The Telegraph executive editor also said the MP was wrong to claim he was "hated" by the newspaper and denied conducting a "witch hunt".
But counsel for Mr Galloway, Mr Rampton QC, accused the newspaper of acting irresponsibly and maliciously.
"If ever there was a case of give a dog a bad name and hang him, this is
it," he said.
The Telegraph had engaged in a "massive exercise in politically motivated character assassination on
a grand scale".
The authenticity of the documents was an important consideration, but newspaper staff should have let Mr Galloway see the papers and given him details of where they were discovered.
It then went on to "smear Mr Galloway all over two successive issues of the Daily Telegraph", Mr Rampton said, "without having given him a cat in hell's chance of putting up a decent defence to what it proposed to say".
He also claimed the main document on which the newspaper's
"massive" coverage was based consisted of "hearsay unproved allegations from an unidentified intelligence officer".
Mr Galloway has branded the story "outrageous" and says he has always opposed Saddam Hussein.
The Telegraph legal team have argued the action was a test case for the "Reynolds defence" - which gives newspapers a defence in libel proceedings if they prove they have done everything possible to verify the story in question.
But Mr Rampton said that defence depended on balance.
Mr Justice Eady reserved judgement and is expected to rule within two weeks.