AS the Leveson Inquiry continues to turn over stones, Alice Sheridan watches with an increasing sense of vindication and horror.

Vindication because she believes the unscrupulous behaviour emerging from the proceedings strengthens her son's earliest claims against News Group Newspapers, and horror that phone hacking should have violated so many thousands of private lives. "Doesn't it put the fear of God in you?" she asks. "It must appal any thinking person that we're becoming a banana republic where once-trusted institutions are found to be corrupt."

We meet within days of Tommy Sheridan's release from jail. At Castle Huntly open prison, on the outskirts of Dundee, he served 12 months of a three-year sentence for perjury committed during his successful defamation case against the now-defunct News of the World in 2006. In early 2010, Sheridan's High Court trial in Glasgow was played out before a crowded Court Four, and on almost every one of its 46 days Alice was in the public gallery to see her son conduct his own defence in what became the longest-running perjury trial in Scottish legal history.

Sheridan, wearing an electronic tag, was back in court last Tuesday, when the Court of Session decided the appeal by lawyers acting on behalf of the News of the World's publishers to reverse the £200,000 damages award against the title in 2006 should remain frozen pending a police investigation into events at the 2010 criminal trial. Sheridan described the ruling as "round one to us" in the battle with News Group Newspapers.

Although she is burdened with continuing poor health, the relief in Alice Sheridan's face is evident from the moment she opens the front door of her tiny flat off Paisley Road West. "I used to be known for my house always looking lovely but this flat is so small you'll have to forgive the clutter." As we settle in the sitting room, Alice smiles more readily than on our last meeting when anguish was held in clenched repose. But now, as the family take time to decompress from the impact of Sheridan's imprisonment on their lives, she reflects that she is still in shock from hearing the jury pronounce that guilty verdict.

Lifelong Catholicism, she says, has seen her through much adversity, and the phial of Lourdes water and rosary beads she carried in her handbag throughout the weeks in Court Four remain close by. But the verdict, she says, rocked her faith to the core. "I was angry with God. Big cheese, me, angry with God, and although I didn't really lose my faith, because faith is a gift, I was so down, so disappointed it was like being in a deep, black hole." That sense of abandonment by the Almighty was like a bereavement. "I stopped going to Mass but then I thought: 'no, no, no these people (those who gave evidence against Sheridan), can't take my faith away. I won't allow it. Evil is something almost tangible, and evil was in that court. Many people have talked about that."

Alice regained enough equilibrium some months later to turn her anger around. "I'm someone who goes through every day, thanking God for everything good that He lets me see, and all the illnesses and operations He's pulled me through – glaucoma, cataracts, breast cancer, spondylitis, fibromyalgia. So I sat down and said: there must be a reason for this, and it's not for me to challenge that."

Long before the High Court trial, that tricky word conspiracy was burned into Alice Sheridan's psyche. "You have to remember that Tommy led the movement against the poll tax that brought down Maggie Thatcher." Later, in the 1990s, the Scottish Socialist Party upheld the militant Left tradition of tearing itself to pieces. "So I always knew knives were going into Tommy's back."

During the High Court trial those sitting near Alice would hear her quiet incantation: "There goes a man who cannot be bought." The steel in that maternal prayer was unmistakable. But all those lurid News of the World sex stories -does the claim of an orchestrated conspiracy really stand up? "Oh, I know it was a conspiracy, and I'll say that anywhere. This case should never have been allowed to go to court.

"If anybody had suggested to Tommy: 'you do a year in prison and when you come out there'll be no News of the World', he'd have said: 'I'll take that deal.' We'd all have taken that deal, no matter the heartbreak. And it's my personal belief that they [politicians, police and the Establishment], knew all along what Murdoch was like. I have watched Tommy go to prison more times than I can count. I've been there myself but on those occasions we had a cause. However, this time was a filthy thing. They [News Group], were trying to rubbish Tommy's name, but they'll never succeed, and history will prove that."

She refers to the psychiatrist Carl Jung's theory of synchronicity. "I'm a fan of Jung, and if you think of what's happened – all these people, who don't know each other, working from different areas to expose what was going on in Murdoch's empire – it was synchronicity, the word Jung coined. And Tommy played a large part in this, by having Andy Coulson (David Cameron's former director of communications, and previously News of the World editor), on the stand."

How does a mother endure what Alice has gone through? "Your heart is breaking but you get through life because you must. The hardest thing was not seeing Tommy in prison. It was walking away and leaving him there." In prison, one of Sheridan's jobs was cleaning the gymnasium and training fellow inmates there in the afternoon. "On Sundays he'd take them running around the grounds, so he kept himself toned. But before each visit I always worried about how he might look. Personally I like him with a wee bit more weight on." And the future? "I don't know what he'll do now. He obviously needs a wee bit of time. It's a big adjustment for both Gail and him, and she's been wonderful. She's kept life magic for the wee one, Gabrielle. But I can't see Tommy ever not standing up for people."

Born in Govan, Alice reflects on her tenement childhood when neighbours looked out for one another. "My granny was the type who always had something for somebody. The enamel jug would be filled up with soup and you'd be instructed to take it to Mrs So-and-So because her man wasn't working and the wean was sick. Or you'd be sent to the steamie with someone's washing because they were ill. That's how I was brought up and I've always been grateful because it balances me, gives me a strength that no one can take away. It's how all my family were raised."

On a side table in Alice's sitting room there is a copy of Sebastian Barry's The Secret Scripture which heart-wrenchingly chronicles the long life of Roseanne McNulty, whose endurance of loss and hurt and betrayal gives her a nobility and rooted sense of place. For Alice Sheridan, in her 74th year, there is comfort in Roseanne's healing appreciation of small mercies. Reason enough, she says, for her to be reading the novel a second time.