Deranged triple killer Joanne Dennehy has failed in a bid for government compensation despite having been "unlawfully" kept in prison segregation for two years.

Prison authorities argued that "uniquely dangerous" Dennehy had to be kept away from other jailbirds because of her notoriety and the escape risk she posed.

There was evidence of a bizarre break-out plot involving plans to use a guard's severed finger to slip through biometric security measures, they said.

But government lawyers admitted that Dennehy had been unlawfully kept in segregation between September 2013 and September last year.

That was because the move had not been formally authorised by the then Justice Secretary, Chris Grayling, Mr Justice Singh told the High Court today.

Dashing Dennehy's pay-out hopes, however, the judge ruled that her segregation did not amount to 'inhuman or degrading treatment' in breach of her human rights.

Keeping her away from other prisoners had at all times been "necessary, proportionate and reasonable", he ruled.

"Uniquely dangerous" Dennehy, 33, is one of only two women in the British prison system serving a 'whole life' sentence.

She murdered Kevin Lee, Lukasz Slaboszewski and John Chapman, whose corpses were found in remote ditches in Cambridgeshire after she butchered them.

With her bloodlust still not satisfied, Dennehy then travelled 140 miles to Hereford where she tried to kill two strangers in a random and cold-blooded act of violence.

She later told a psychiatrist that she started killing to "see how it would feel - to see if I was as cold as I thought I was...then it just got more-ish."

Dennehy, of Orton Goldhay, Peterborough, was handed the "life means life" sentence at the Old Bailey in February 2014 after admitting three murders and two attempted murders.

The judge who sentenced her said she had shown no remorse, branding her a "cruel, calculating, selfish and manipulative serial killer".

At the High Court, her barrister, Hugh Southey QC, described the psychopathic lifer as a "vulnerable" inmate due to her history of severe personality disorders.

He challenged HMP Bronzefield's decision to keep Dennehy segregated from other inmates - entailing long periods of isolation.

The incarceration was taking a heavy toll on Dennehy, he told Mr Justice Singh, leaving her "tearful and upset" and at times self-harming.

The initial reason for segregation focused on fears of a prison break by Dennehy and other inmates dating back to her time on remand, the court heard.

Security staff at the jail believed there was a credible escape plan involving two other prisoners and "a plan to seriously assault or kill a member of prison staff".

One aspect of the alleged plan was that "the finger of an officer would be cut off in an attempt to deceive the biometric security system at the prison".

But Dennehy insisted the plan was nothing more than a "doodle" found in her diary and, after an investigation, police decided to take no further action.

Mr Southey argued that Dennehy should be be paid compensation as "just satisfaction" for violations of her human rights.

The prison authorities accepted in the light of a Supreme Court ruling that Dennehy's segregation up to September 4 last year was in breach of prison rules in force at the time.

And Mr Justice Singh accepted that segregation without the Secretary of State's authority breached Dennehy's human rights.

However, he went on to rule that Dennehy's segregation was 'at all material times' necessary and proportionate and therefore 'lawful at common law'.

Government lawyers said Dennehy had to be segregated because of the "nature of her offending" and the risk she posed to others.

They also disclosed that Dennehy is now undergoing a "phased reintegration" to normal prison life.

The jury at Dennehy's trial heard that she had "cast a spell" over some of her victims.

She had met one of them, Lukasz Slaboszewski, just days before his killing at a property in Peterborough on or soon after March 19.

He had told friends he had met an "English girlfriend" and it is thought he went to meet Dennehy expecting sex.

She stabbed him in the heart before depositing his corpse in a wheelie bin.

On March 29 2013 she stabbed John Chapman at the block of bedsits they shared in Bifield, near Peterborough.

Mr Chapman, a Falklands War veteran, was fearful of Dennehy and described her to friends as the "man-woman".

She then arranged to meet Mr Lee - her landlord with whom she was having an affair - before also stabbing him to death.

Mr Lee's body - wearing a black sequin dress and arranged in a sexual pose in a "final act of humiliation" - was discovered in a ditch near Newborough on March 30.

While on the run in Hereford, Dennehy and an accomplice randomly selected two dog walkers - Mr Bereza and John Rogers - for attack.

She leapt from a car and repeatedly stabbed each of them. Both men suffered severe injuries but survived the attacks in Whitecross and Hunderton.