THREE former RUC officers who investigated the murder of Belfast solicitor Pat Finucane are to sue the PSNI chief constable over failures in the police investigation.

The Irish News has learned that former CID officers, including Trevor McIlwrath, Johnston Brown and retired Detective Superintendent Alan Simpson lodged legal papers with the High Court in Belfast late last year.

The dramatic move comes as the family of the murdered human rights solicitor continue their campaign for a public enquiry into the murder 27 years ago.

The 38-year-old lawyer was shot 14 times by two UDA gunmen at his north Belfast home, in February 1989.

His widow Geraldine was also injured during the attack.

The former officers claim they were unable to solve the case, one of the most controversial of the Troubles, because RUC Special Branch obstructed their investigation.

Several of the people centrally involved in the Finucane murder were Special Branch and British army agents.

In September 2004 UDA man Ken Barrett, who was a Special Branch informer, pleaded guilty to his murder.

Solicitors for the former detectives claim "the foregoing loss and damage was caused and/or contributed to by the wrongful acts/omissions, neglect and default of the defendant."

They claim that the "acts and/or omissions constituted a conspiracy by the use of unlawful means, misfeasance in public office, breach of confidence, defamation, malicious falsehood, breach of statutory duty and or the negligence of the defendant, their servants and agents in relation to that investigation".

The basis of their claim is that the alleged omissions were incompatible with several articles contained in the European Convention on Human Rights, including the right to life.

Alan Simpson, the retired senior officer who headed up the Finucane investigation, said he has been left with a "deep sense of betrayal" that has stayed with him for the past 27 years.

"I have all of these terrorist organisations, I have the IRA, the INLA, the UFF, the UVF, the Red Hand Commando all doing murders in north Belfast," he said.

"I do not need Special Branch coming up and organising one (murder) and then standing in a room with me keeping quiet and all the time knowing the true facts and leading me astray."

Of his decision to take legal action he said: "I want some sort of satisfaction, some remedy in court".

Mr Simpson, who served in the RUC for 36 years, claimed senior Special Branch officers, who he dealt with on a regular basis, knowingly withheld information from him during his investigation.

He also claims that within days of the murder he received a visit from one senior RUC man who advised him not to get "too deeply involved in this one".

Mr Simpson said that three days after the killing a senior Special Branch officer visited his incident room but told him nothing even though it has emerged the officer knew everything about the case.

"Knowing from de Silva now, he knew everything about that murder, who was involved, how it was carried out. He stood there with his funeral face and as I have often said he had more loyalty to the UFF murder gang than he had to me."

Mr Simpson also maintains that Special Branch provided him with a list of suspects - including the name of one who was in jail at the time of the murder.

"They sent me a bum steer," he said.

In recent years the Finucane family has campaigned for a full independent inquiry into the murder. They were bitterly disappointed when in 2011 Conservative Prime Minister David Cameron reneged on a British government promise to hold an inquiry.

Instead, Mr Cameron asked British QC Desmond de Silva to carry out a review of material relating to the case.

In 2012 his report confirmed that state agents were involved and that it should have been prevented.

He also concluded that there was no overarching state conspiracy.

The Finucane family later rejected the review findings, branding the process a "sham".

Last year a High Court judge ruled that Mr Cameron acted lawfully in refusing to hold a public inquiry.

The family has since appealed this ruling.

A solicitor acting for the three men last night said they felt they had not other option but to take legal action.

"There isn't a forum for this narrative to be dealt with and heard, these particular ex officers have felt they have little if any option but to go down this legal route through a civil action," Kevin Winters said.

"There is no other option as matters stand and any attempt to articulate what they have been through has been met with indifference or worse arrest.

"This litigation represents a challenging alternative narrative on collusion. Up until now it has not been articulated enough through the courts.

"For the very first time this case changes that."