There was never a hope for Patricia Cahill and Karyn Smith as long as they protested their innocence. Smith would tell anyone who cared to listen through the bars in the Bangkok prison that, yes, she had pleaded guilty. But she was pressured into confessing, see?

Otherwise she might have faced the death penalty. Really, she was innocent. Cahill, too, insisted she was innocent.

And as long as the girls clung to that version and campaigners back home protested their innocence, the gates stayed shut.

The road to freedom began on Bonfire Night last year when, in an exclusive interview with the Express & Star, Patricia Cahill finally admitted her guilt.

The truth spilled out in a tearful face-to-face meeting with feature writer Ian Cobain, winner of an Amnesty International journalism award for another human-rights investigation.

Cobain met both Smith and Cahill at the notorious "Bangkok Hilton" prison. The women wore prison uniforms of blue shorts and cotton smocks. Smith quit the interview after a few minutes.

But Cahill stayed and, when the standard 30-minute visiting time was up, begged the warder for longer to talk with the journalist.

It was then that she confessed, for the first time, that she knew she had been smuggling.

Until then, both girls had claimed that they had been duped after a drug syndicate offered them "the trip of a lifetime" to the Far East.

"I knew I was carrying something," Cahill told Cobain. But she insisted she did not know it was heroin.

"It could have been gold or ammunition. I did not know anything about drugs at that time."

The teenagers were arrested at Bangkok Airport in July 1990 and charged with carrying 67lbs of heroin with a street value of £4 million.

Karen Smith, then 19, pleaded guilty and was jailed for 25 years. Patricia Cahill, 17 at the time, pleaded not guilty but was convicted and sent down for 18 years.

"I blame the people in Birmingham who set me up," Cahill told the Express & Star. "But I also blame myself. I see now that I was in a position to prevent everything that happened to me."

Her confession effectively torpedoed the campaign to prove the girls' innocence.

Back home in Birmingham, Cahill's lawyers had been protesting that the "appalling Thai legal advice" which persuaded Smith to plead guilty had sabotaged the other girl's case.

By this summer the girls' campaign was going in two separate and contradictory directions. And unknown to anyone, Downing Street was seeking a pardon for both. Smith still claimed to be innocent. Her solicitor, Stephen Jakobi, was alleging that Thai police had planted the drugs on her.

But Cahill was desperately seeking a pardon. Her father, Paddy, who a year earlier had claimed his daughter had been beaten up and forced to take part in the trip, publicly apologised to the Thai prime minister over the drug-plant allegations.

This week came a final bizarre twist when the Bishop of Birmingham, the Rt Rev Mark Santer intervened, pleading for clemency but yet again repeating the charge that the drugs had been planted.

In a desperate appeal from Bangkok, both girls told the "do-gooders" to mind theirown business.

More significantly, for the first time, Karyn Smith refuted the drug-plant story.

The process of confession that began with an Express & Star exclusive eight months ago was complete. Within 48 hours, Karyn Smith and Patricia Cahill were pardoned.