What is the double jeopardy law in I Fought The Law?

Sheridan Smith is set to star in the upcoming ITV drama, I Fought The Law, portraying the role of grieving mother Ann Ming.

Ann endured a 17-year battle for justice after discovering her daughter Julie Hogg's lifeless body hidden beneath a bath in 1989.

Julie was just 22 when she was strangled at her Billingham home by William 'Billy' Dunlop, but two juries failed to reach a verdict on his guilt in 1991.

While serving time for another offence, he brazenly bragged about the murder to a prison officer. At that point, he was shielded by the double jeopardy law which stopped someone from being tried again for a crime they had been cleared of, reports Chronicle Live.

• READ MORE: ‘I discovered my daughter’s body after she was murdered and her killer didn't get jailed for years’

• READ MORE: I Fought The Law ITV release date, cast, episodes and real life story behind drama

However, Ann Ming made it her mission to change this archaic law so that serious criminals could face retrial if new evidence or a confession emerged.

Thanks to Ann's relentless campaign, the law was altered in 2005 and Dunlop, who is now serving a life sentence, was convicted under the revised law a year later.

His conviction marked the first under the updated law, which had been in place for over 800 years.

A reconsideration of the double jeopardy law was proposed by Lord Macpherson following the murder of Stephen Lawrence and the unsuccessful prosecution of his suspected killers.

Ann joined the fight for the law to be abolished and in 2001, the rule was examined by the Law Commission.

The Criminal Justice Act 2003 outlines how a Court of Appeal can mandate a retrial when there is new and compelling evidence relevant to the guilt of the acquitted individual.

In the case of Julie Hogg, the fresh evidence was Dunlop's confession while in prison. At that time, he could only be charged with perjury.

Ann's lengthy struggle is the focus of ITV's I Fought The Law and, after viewing the series, she told the BBC: "There were cries all the way through it.

"All I was doing was reliving it all and I knew what it felt like inside. Sheridan portrayed me as though she was inside me."

I Fought The Law starts on ITV on August 31 at 9pm