The sister of Gerry Conlon, who was wrongly accused of the Guildford pub bombings, is to sue the PSNI and Surrey Police.
Bridie Brennan is taking the legal action against the two police forces for conspiracy to wrongfully arrest, detain, interrogate and charge her brother.
Legal proceedings are due to be issued in the High Court in Belfast.
She is serving a writ of summons on the PSNI (the successor authority to the RUC) and Surrey Police.
Her lawyer, Christopher Stanley of KRW Law, said Ms Brennan is "determined to hold the RUC and Surrey Police to account for the torture inflicted on her brother".
The Guildford Four, which included Mr Conlon, Paul Hill, Paddy Armstrong and Carole Richardson, were falsely accused of two pub bombings in Guildford in October 1974 that killed four British soldiers and a civilian.
They were released in 1989 after 15 years behind bars.
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Members of an IRA unit – the ‘Balcombe Street Gang’ – later confirmed they were responsible, but were never charged.
Mr Conlon’s father Guiseppe Conlon, who was a member of the Maguire Seven, died in an English jail in 1980 aged 56.
The Maguire Seven were all convicted but were also later proven to be innocent of involvement in any part of the attack.
Ms Brennan's legal team said she is suing the PSNI and Surrey Police for conspiracy to wrongfully arrest, detain, interrogate and charge her brother and will "make it clear that Gerry Conlon was tortured in order to obtain his confession".
In a statement, KRW Law said Mr Conlon, who died in 2014 aged 60, was arrested in Belfast following the Guildford Pub Bombings and detained and interrogated on the basis of ‘intelligence’ from the British Army and the RUC.
They add that intelligence shared between London Metropolitan Police Special Branch, Surrey Police CID and the RUC led to Mr Conlon being detained in Belfast on November 30 1974.
In addition, Surrey Police had a confession from Paul Hill, who was also charged and convicted of the Guildford Pub Bombings.
His confession was obtained by way of coercion and duress and named Mr Conlon.
KRW Law add that at Springfield Road RUC Station, Mr Conlon was beaten and tortured, including being subjected to wall standing, deprived of sleep and food and his family threatened.
They say the treatment Mr Conlon "suffered was similar to the institutionalised torture – the five techniques - endured by The Hooded Men".
They said that analysis of Sir John May’s report into the miscarriages of justice arising from the pub bombings in England in 1974, commissioned by the British government and published in 1994, revealed that the arrest, detention and interrogation of Mr Conlon in Belfast and Surrey led directly to his conviction.
Ms Brennan's legal team said while "she knew her brother had been ill-treated and wrongfully convicted and imprisoned, she did not realise his fate started in a Belfast police station".
They say the treatment of Mr Conlon by the police has "re-traumatised" her.
"Bridie Brennan knows that her civil action will be considered to be part of the ‘Legacy’ and therefore will be dismissed by the policing authorities as a matter to be dealt with under the draconian and derided Legacy Bill," the statement added.
"She contests that designation.
"She believes that there is a continuing miscarriage of justice, regarding the wrongful imprisonment of her brother when the criminal justice authorities – the police, the prosecutors, and the judiciary – knew his confession was false and that an admission of responsibility by the actual perpetrators was known.
"Bridie Brennan has faith in the legal process in Northern Ireland to facilitate her right to access justice in the name of her brother, Gerry Conlon."
Mr Stanley, a litigation consultant, added: “Serious questions about the 1974 pub bombings in Guildford and Birmingham continue to be unanswered.
"Specifically, the question of who was responsible.
"The families of those who were murdered, and the families of those who were wrongly accused of those murders, continue to seek truth, justice and accountability.
"Bridie Brennan knows that her ‘window of opportunity’ may be closing with the pall of the Legacy Bill – as do many others – but she is determined to hold the RUC and Surrey Police to account for the torture inflicted on her brother in order to obtain a convenient confession whilst the real perpetrators remained, and remain, free.”