Father Patrick Lawson opens the front door of his mother's house in the outskirts of Glasgow, fag in hand, the watchful eyes of a jewel-adorned Mary Immaculate statue following from the corner of the hall.

His smart grey suit and clerical collar jar. The collar hasn't been much in evidence since he was removed as parish priest of St Sophia's in Galston, Ayrshire, in September 2013. His dismissal followed an 18 year dispute which erupted after he spoke out as a seminarian about Fr Paul Moore, who sexually assaulted him and abused two altar boys. Today, Lawson is flying to London to see the Papal Nuncio, Archbishop Antonio Mennini, Pope Francis's representative to Britain. It is a last ditch effort to avoid an historic case: an industrial tribunal for unfair dismissal against the Catholic Church. Barring last minute intervention, the case begins on Thursday and could change the employee status of priests in the whole of Britain.

The Nuncio's invitation is secret. Not even Lawson's new bishop, William Nolan, knows. Nolan, only recently appointed, has continued the fight of his predecessors - Bishops Maurice Taylor and John Cunningham - against Lawson, without even meeting him. In fact, just days previously, he had issued Lawson with a coldly menacing canonical letter informing him that persisting with the tribunal, would provoke further action against him. Urging obedience, Nolan wrote, "Taking action against the Diocese in a civil tribunal would not be in the spirit of the priesthood". An interesting argument given that Nolan has two outstanding civil cases against another priest, Matthew Despard, currently in the Scottish courts. Resorting to civil action may be a matter for canonical censure for Lawson, but not, it seems, for Nolan.

Lawson feels he has no choice. Civil law granted him legal aid. The Catholic Church's supreme court, the Signatura, on the other hand, wrote - in Latin - demanding 1500 euros to hear the case plus thousands of euros for one of the few elite lawyers allowed to appear at the Signatura. Lawson couldn't afford it and appealed for help. The reply? A letter telling him the case was now dropped because he hadn't paid within two weeks. It triggered a triumphalist letter from Bishop Nolan to parishioners telling them Lawson had "lost" the case. "When I saw that letter," says Fr Gerard Magee, a fellow priest of the diocese, "I thought, he's never met Pat, never shaken his hand, never sat down with him. He will regret that."

Lawson's removal followed his decision to arrange cover for the smaller of his two parishes, St Paul's, Hurlford, after becoming ill with cancer. Doctors had advised him to reduce his duties but the Diocese's Vicar General, Willie McFadden, went to the smaller parish and encouraged complaints. Twenty three were received, some of which were not even from parishioners. These 'complaints' sparked outrage in the community and over 300 supportive letters were sent to the Bishop. Lawson was still removed on the grounds he had caused "division" and was too ill to work, despite doctors' written assurances that he simply needed to do less. "They waited until I was at my weakest," says Lawson. "It didn't matter that it took them eighteen years."

Lawson's appeal to the tribunal is for unfair dismissal. But for the case to be heard, the tribunal must first decide if priests are employees. It is a battle that is unlikely to be won immediately and may well be the subject of years of challenge up to the Court of Session. Fr Magee will appear to give evidence. "Everything we do centres round employment," he argues. "They recruit us; they appoint us; they pay a stipend; pay our national insurance; give us a pension, a house and even pay for our funerals. Why would you do all that for someone self-employed?"

Magee risks censure for speaking but says the issues are important. "I like and get on with Pat Lawson but I am not a supporter of him as such. I am a supporter of the truth." So what IS the truth? "Pat Lawson was removed from his parishes not because he was neglectful in caring for the people, in fact he was unwell at this time and had alerted the bishop of this, but rather because he 'blew the whistle' on Paul Moore. Those responsible for his removal are all good friends with Moore and support him, even though they know that he has confessed to child abuse. I made my thoughts known to the Papal Nuncio in writing on several occasions. There is much more to this than meets the eye."

Further censures are likely to include preventing Lawson saying mass publicly and possibly removing the small pension the church gave after forcing him to retire. "It feels like blackmail," says Lawson. Canon law controls, silences, humiliates. It is powerful; some suspect this latest threat to Lawson will lead ultimately to laicisation. "But how can I be silent?" asks Lawson. "I can't be part of this poison or manipulation any longer."

Mary Immaculate, with her vase of fresh flowers, stands guard outside the sitting room. Inside, Lawson's 85 year old mother, Rose, prepares for communion from her son before he leaves. Rose is the holiest woman you could meet. Her lips move constantly in prayer and everything stops daily at 3PM for her prayer of adoration to the Divine Mercy. A senior priest told Lawson he must not challenge the church for Rose's sake. His mother would be so upset by bad publicity and he must "offer up" injustice. Besides, he would burn in hell if he lost his priesthood. But Rose, who is in the preliminary stages of vascular dementia, is agitated this morning. "I cannot believe how they have made him suffer," she says, fighting for breath. Her eyes burn. "If they do not do the right thing by him, it must go all over the papers."

Lawson has a white envelope with the blue seal of the papal nunciature on the back. It is stuffed with crisp bank notes for his travel to London. On the way to the airport, he opens the car window. Is it okay to smoke? No. Lawson grins, knowing I don't mean it, then puffs. Why isn't he more obedient? Like his Bishop ordered. But Lawson judges the appropriacy of obedience. It is not blind obedience. "It is important to distinguish," he wrote to Nolan in response to threats of further action, "between indulgent self-will and informed conscience; between the relinquishing of personal responsibility and the exercise of mature judgment."

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THE INVITATION TO the Nunciature has been unconventional to say the least. Lawson has written to the Nuncio, and the Pope, for years and been ignored. Last month, he contacted Pete Saunders, head of the National Association for People Abused in Childhood (NAPAC) and a lay member of the papal commission on abuse. Saunders is threatening to quit the commission if real change isn't implemented. Currently, members are furious about the appointment of Bishop Juan Barros of Chile, who is said to have been present while another priest abused children.

When Lawson contacted him, Saunders was horrified by his story. "I want abusers, and anyone who protects them, out of the church. I think Patrick has suffered terribly. The church needs people like him." He agreed to champion Lawson's cause in Rome. "I am very privileged to have access to the Pope - and I also know there are layers of people who never let things get near the Pope." When he informed the Nuncio he intended getting documents directly to the Holy Father, Mennini sent a stuffed envelope to Lawson and an immediate invitation.

Wimbledon, London. An opulent mansion: wood panelled halls; paintings; a sunken drawing room with antique furniture, overlooking a terraced garden. The papal nuncio enters, white fluffy dog in arms, followed by his Mexican secretary, Monsignor Javier Herrera. To Lawson's discomfort, Mennini persistently kisses him and strokes his face throughout the meeting. It's not how it's done in the West of Scotland.

Mennini, whose father headed the Vatican bank, is a diplomat. Lawson must not cause scandal with this tribunal. What is causing scandal? Lawson demands. Speaking out about abuse? Or the Bishop's abuse of power? After all, Paul Moore abused children but has never had a single disciplinary action against him. He has been retired, bought a house, given a pension, visited, looked after. Yet when Lawson was in hospital, not one member of Galloway Diocese visited him. "Father! Father!" exclaims Mennini, clutching his hand. "Calm down - you are a Roman!" But he WAS calm, insists Saunders. "Patrick conducted himself in an exemplary way. He was there to seek justice for the very great injustice he has suffered and he was very cool."

Mennini reaches for the phone. He will call Bishop Nolan. "It was bizarre," Lawson recalls. "He told Bishop Nolan he should meet with me 'like a spiritual father'. But I could hear the Bishop's voice at the other end. I got the impression he was furious." Bishops consider themselves autonomous. Nobody interferes in their fiefdoms. But Mennini insists Fr Patrick will be in touch to arrange a meeting. They must start a fresh page. He rings off. "The nunciature is at your disposal," he tells Lawson.

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IT IS LATE when Lawson returns from London. Rose is in bed, a tiny figure against the pillows. Will I help Patrick when she is no longer here? Yes, but the rate he's smoking, she'll outlive him anyway. "I'll give up," says Lawson. When? "When bishops stop killing me." After a year away from the church, he realised he was dying slowly at their hands. He returned to university to complete a doctorate in counselling psychology, intent on helping the abused. But it's been a tough academic year with the church letters and battles, the publicity and humiliation, the pressure of being Rose's main carer.

Next day Lawson emails Nolan asking for a meeting in the light of the Nuncio's request. His 'spiritual father' replies in emails seen by the Sunday Herald that since Lawson hasn't dropped the tribunal, canonical action is on-going, and he will not meet Lawson without officials present. What happened to starting a clean page? Lawson is unsurprised. He's had 18 years of it. The replies zing back and forth between him, the Nuncio and Nolan, but Nolan's insistence on absolute control prevents progress. Eventually, the Bishop asks for a letter of apology. "What for?" writes Lawson. "Being sexually assaulted? Or unfairly dismissed?"

He phones the Nuncio. His intervention has resulted only in a power battle between him and Nolan and there will be no letter of apology. "If you take my priesthood," he says, "so be it." The words are not careless. Priesthood once meant everything to Lawson. "But they can't take God," he says. He still believes? "Absolutely. But given the evil I have experienced, I just believe He's moved outside of the church."

When contacted, Bishop Nolan insisted, "I do not want to comment." Peter Kearney, Director of Communications for the church, said that Father Lawson's refusal to accept church decisions, "is contrary to his obligations as a priest to respect the Pope and his Bishop. Canon Law obliged Bishop Nolan to advise him of this and urge him to reconsider." As far as the Bishop's own civil actions were concerned, they were, "the only means" of evicting a priest from a parish house.

As far as Fr Lawson is concerned, the tribunal is his only means too. But he knows justice will be hard to achieve. When he first took the action, a key decision had been taken in the English courts giving Methodist priests employee status. Things looked positive. But that decision went to the Supreme Court - normally the most liberal - and was overturned. There's still a chance of victory but Lawson is unconcerned about the verdict. Victory is being true to yourself. "This is not about winning," he says. "This is about speaking the truth." ENDS