Jason Dunn’s case came to light after he committed an offence at HMP Gartree, near Market Harborough, Leicestershire, by throwing the contents of his slop bucket in the face of a female guard as she opened his cell door.
Dunn was only a foot away from the guard and some faeces and urine went into her mouth.
He appeared via video link at Leicester Crown Court to face a charge of administering a noxious substance. He has now been jailed for another two years.
Dunn was 19 when he was jailed for the mobile phone robbery – he is now 34 with no apparent release date.
His 24-month sentence was part of a now defunct Imprisonment for Public Protection (IPP) order, meaning he could only be released when the Parole Board no longer considered him to be a danger to the public
IPPs were abolished in 2012 but some offenders who received them are still locked up.
Dunn was entitled to annual reviews of his imprisonment but may not have realised he could apply for his case to be studied due to his poor mental health.
Prosecutor Sarah Phelan said: “It was directed at her face and went into her mouth and eyes and all over her clothes.
She was unwell and unable to carry out her duties and had to have the assistance for anxiety and depression as a result of the incident.
“It’s not known when she returned to work.
“In interview, the defendant made full admissions saying he’d been ordered to carry out the attack by another inmate, whom he was in debt to for spice (the drug) for £100 and if hadn’t carried out the act he would have been slashed.”
Defence barrister John Simmons said Dunn’s situation was now being “given attention” as he admitted his client is “not blessed with great intelligence”.
He said: “I’m afraid there are similar cases to Mr Dunn’s with others having been given similar sentences like his.
“He was 19 when he was convicted and the offence involved the aggravated theft of a mobile phone.
He’s become thoroughly institutionalised. Almost the entirety of his adult life has been behind bars and he’s not really known why.
“He may have had mental health problems and he’s never sought to question it.
Sentencing Dunn, Judge Robert Brown said: “The reason you have been in custody for so long is not a matter for today’s hearing.
“This was a serious assault on an officer in the prison service who was doing a difficult job.
“It’s difficult to think of a more disgusting thing to do, throwing faeces and urine at her, some of which goes into her mouth. I hope you’re ashamed.”