As she approaches her 79th birthday, national treasure Dame Judi Dench looks certain to be gifted a seventh Oscar nomination for her tour-de-force portrayal of a guilt-stricken mother in Philomena.

It's a compelling performance of deep emotion based on a true story that deftly tugs the heartstrings without resorting to emotional manipulation or cloying sentiment.

Dench is complemented by Steve Coogan as a cynical and world-weary journalist, who initially scoffs at the suggestion that he should pen an article about the matriarch and her heartbreaking ordeal.

"Human interest stories are a euphemism for stories about weak-minded, ignorant people," he proclaims dismissively.

The tender and unexpectedly touching relationship that forms between these two characters from different generations and backgrounds provides Stephen Frears's uplifting film with its emotional thrust, as the search for answers moves between continents.

Coogan's script, co-written by Jeff Pope, is lean and peppered with earthy humour, whether it be the much abused heroine reliving the ecstasy of her first sexual experience or her encouraging the journalist to jump into the back seat of a rental car.

"There's plenty of room. It's a Vauxhall Cavalier," she trills.

The incredible road trip begins when Jane Lee (Anna Maxwell Martin) discovers her mother Philomena (Dench) fell pregnant as a teenager in 1952 Ireland and was forced to give up the baby to the sisters at Roscrea Abbey. Jane pitches the story to former Labour advisor turned BBC journalist Martin Sixsmith (Coogan).

After a reality check from his wife Kate (Simone Lahbib), Martin agrees to help Philomena track down her boy.

"I'd like to know if he thought of me," Philomena tells Martin. "I've thought of him every day."

Using his connections, Martin takes Philomena to Washington DC to sift through official documents, hoping for a breakthrough to reunite the old woman with the son she never wanted to give up.

Throughout, Philomena clings to her faith, lighting a candle for her child. However, Martin cannot conceal his contempt for religion, telling Philomena, "It's the Catholic Church that should be going to confession, not you!"

Directed with a light and assured touch by Frears, Philomena celebrates the power of hope to heal old wounds.

Dench is magnificent and Coogan jettisons most of his Alan Partridge tics in support, gradually warming to Philomena and her upbeat outlook on life.

"Just because you're in first class doesn't mean you're a first class person," she tells him during a long haul flight in economy class.

Tears flow freely as the eponymous heroine discovers the fate of her boy, seizing upon every nugget of information, no matter how banal, as if she had just won the lottery.

We certainly strike it very lucky with Frears's wonderful picture.