MAXINE PEAKE as Mrs Mary Whitehouse has a look that can quell: shrewd, appraising, contemptuous, almost gleeful in her relishing of a fight. She turns it directly on the audience at her first appearance, her bespectacled face appearing through floral stage curtains in an attitude that declares her steeliness to take on all comers in her war against obscenity.

Caroline Bird’s play The Last Stand of Mrs. Mary Whitehouse is anchored in the 1977 prosecution for blasphemous libel which she brought against Gay News for publishing a graphic poem by James Kirkup in which a Roman centurion fantasises about having sex with Jesus after taking his body down from the cross. The poem still shocks when we hear it read: she was canny in picking something certain to rouse a disgust or discomfiture not confined to Christians alone.

John Smyth QC led the prosecution. “He led Christian camps for public schoolboys,” she says in innocent admiration for the barrister: an irony not lost on the audience. But this isn’t a courtroom drama, and the trial itself is not the dominant thing. More scenes take place in her garden, a one-woman operational base from which she views distant protesters through binoculars and offers baffled journalists sponge cake from a trolley.

And that is part of the paradox so cleverly presented by Bird’s play, directed by Sarah Frankcom. Whitehouse rails throughout against “the Homosexuals” as “an abomination against God”, “clearly mentally ill”, and “wanting the destruction of the family”. Her mind is closed: her Evangelical conviction prohibits any other consideration. This is her mission. “My life is not about me,” she declares. “It’s about giving my life to the Lord.”

So, the most agonising scene is a clumsy conversion-therapy session conducted with a deeply troubled gay man by a zealous and younger Mary. She is earnestly ticking off the stages on her clipboard: the desperate howl and vomiting into a bucket which is Step One — Conviction; the “burden of sin falling off your shoulders” which is Step Two — Conversion; culminating in Step Five — to “prevent Backsliding”.

Yet she genuinely wants to comfort them all. People fall throughout the play into her grandmotherly arms. “Jesus is the last hope these men have;” “Even Homosexuals have hope of salvation,” she declares. Her own vulnerability breaks through when she speaks to a feminist journalist of the death of newly born twins (she abhorred abortion). The closing scenes depict a resentful Mary, wheelchair-bound in a care home and confronted with the tenderness of a gay carer who refuses to be ruffled.

The play captures all the permissiveness of an age that gave birth to the National Viewers and Listeners Association and the Moral Rearmament movement. Samuel Barnett deftly plays a parade of 15 characters, including distressed mothers, anguished clerics, and public figures, who include (riotously) Margaret Thatcher.

Mrs Whitehouse won the trial, declaring to the press: “I am rejoicing because our Lord is no longer vilified.” She had earlier given voice to what is, perhaps, the most telling line in the play: “If they can bag Christ, they’ve won.”

At Nottingham Playhouse, Wellington Circus, Nottingham, until 27 September. Phone 0115 941 9419. nottinghamplayhouse.co.uk