Last week he was on screen and in print castigating the Home Secretary over the 'shameful' decision to extradite to the United States two of his clients, former followers of the Bhagwan Shree Rajneesh, to face charges of conspiracy to murder.
He was in a recent documentary after unearthing new evidence that could bring a reprieve for a Scotsman on death row in Ohio. In a highly publicised case last year he won the acquittal of Stephen Owen, who shot and injured the lorry driver responsible for killing his son. And then there is his most infamous client, Myra Hindley. She has now served 28 years for the child killings she carried out with Ian Brady.
Mr McCooey, 45, became her solicitor five years ago, when she approached him. 'I won't pretend it was a straightforward decision. I asked my wife if she had any objections. I thought we might come in for some abuse,' he said.
'But I have to say I have never regretted it. I have seen Myra many times. I am fully aware that her crimes were quite horrendous but I feel sure that she is now a completely different woman who should be considered for parole.'
Eloquent and forthright on behalf of his clients, Mr McCooey becomes reticent, almost apologetic, when answering questions about himself. But others are open with their praise. One colleague described him as 'unrelenting in his fight for justice'.
Lord Denning described him as 'really a very good sort of person. One of the most energetic and able lawyers, who will work for nothing if he thinks the cause is right'.
The unlikely couple - the former Master of the Rolls and a country solicitor - became friends when, as members of the Lawyers' Christian Fellowship, they joined forces in a vain bid to take on the Church of England over the ordination of remarried divorcees. It proved one of Mr McCooey's rare defeats.
The church nearly claimed Mr McCooey for itself, when he gave up his law studies to take a degree in theology. But five years later, in the mid-1970s, he 'realised that my real leaning was towards criminal law. But I am a committed Christian and my faith is part and parcel of my life and work.'
It was the church that brought Mr McCooey the big case that was to become the foundation stone of his reputation. A computer operator aged 19 was charged with starting a fire at a Miami hotel in which two people died, and faced a possible death sentence. Her desperate parents, who knew Mr McCooey through the church, asked for his help. He went to Miami and unearthed forensic evidence to prove her innocence - the fire was caused by an electrical fault.
Watching a television documentary about the Ohio case prompted Susan Hagan and Sally Croft to contact Mr McCooey to represent them when, five years after they had left the Bhagwan's Oregon commune, they were charged with plotting to murder a US attorney.
Other lawyers might have considered the case politically hopeless - Britain has never refused a US extradition request - but Mr McCooey determined the charge against the two women was so manifestly unjust he enlisted the help of the great and the good to stop it. Last week, with the Home Secetary's announcement, it looked as if he had failed. But even now he refuses to give up. The women are seeking a judicial review of Mr Clarke's decision.
Yesterday Ms Croft said: 'He is incredibly committed to his work. He makes you feel he has faith in you.'
Mr McCooey said: 'Defendants need to believe that you believe in and care for them. When it comes to Judgement Day, it's not about how clever you are or how important. It's about whether you helped the least person - you know, those less fortunate. My task is to stand up for such people and do all I can to help.'
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