A man who confessed to responsibility for the deaths of 26 people in a series of arson attacks in the 1970s was an “unreliable narrator”, a court has heard.

Peter Tredget, previously known as Bruce Lee and Peter Dinsdale, has been detained in a secure mental hospital since 1981 after pleading guilty to 11 counts of arson and 26 counts of manslaughter on the basis of diminished responsibility over fires set in houses  around Hull between 1973 and 1979.

The 61-year-old is appealing against his convictions at the High Court in London, following a referral from the Criminal Cases Review Commission (CCRC).

During a previous Court of Appeal bid in December 1983, judges upheld most of his convictions, but they quashed one count of arson and 11 charges of manslaughter in relation to a fire at an old people’s home in Hessle in 1977.

In his new appeal, which is being challenged by the Crown, Tredget’s lawyers argue that due to his “psychological vulnerability” at the time of his 1980 confessions he was an “unreliable narrator” and no “credence” should be given to his guilty pleas.

His barrister, Tim Barnes QC, told the High Court on Monday: “Absent the confession, there is simply no evidence which would have led to this appellant being charged, let alone to him being convicted.”

Mr Barnes told the court that Tredget, who was previously assessed as having an IQ of around 73, was described as “highly suggestible, unreliable” by a psychiatrist, who said it was “difficult to place any credence on what he says”.

The court also heard he had been on a “substantial” alcohol “bender” before his arrest and first police interview in June 1980, which was conducted without a solicitor or a “responsible adult” present.

Mr Barnes said in written submissions that Tredget’s “low IQ, learning difficulties, personality disorder and other personal characteristics which existed at the time of the confessions and at the time of trial undermine the credibility of the confessions and the pleas.”

He told the court that expert analysis of Tredget’s written confessions taken down by police reveal that they contain passages that were “completely rewritten” by a senior officer.

Mr Barnes highlighted the fact that Tredget frequently changed his story when speaking to the police and doctors over whether he had started the fires and for what reasons.

Some explanations he gave at the time were that it was for financial reasons, that it was due to his upbringing, that he was an accomplice to a more skilled arsonist, that he was drunk or that fires made him feel relaxed.

The court heard Tredget, who has “unswervingly” denied responsibility for all the fires for the last 35 years, was previously assessed as “semi-paralysed down the right side”, with a “withered” arm and a limp.

“The degree of physical dexterity required to access some of these properties, carrying a container of paraffin and setting the fires in the way the prosecution allege, would have been extremely difficult if not impossible for someone with such physical disabilities,” Mr Barnes said.

“In respect of all the fires there is no identification evidence and no forensic evidence to connect [Tredget] with any of them,” Mr Barnes also noted in written submissions.

He pointed out that fire experts had found that, with the exception of a blaze at Selby Street in Hull, it was “impossible… to exclude an accidental cause of each of the fires”.

“The coincidence of 10 separate fires, each of which are alleged to be arson, having an alternative and credible accidental explanation is vanishingly unlikely,” he said.

He told the court that the detail of some of Tredget’s confessions “just does not fit with the facts as we know them”.

One fire at Gorthorpe, in which a 13-month-old baby died, would have involved Tredget travelling for two hours by train and on foot from a children’s home in the evening to make the alleged arson attack.

“As a youth with a withered arm, limping and carrying a container of paraffin, his presence in the streets of Hull would have likely drawn attention,” Mr Barnes noted.

The court heard that a five-year-old child in the building admitted to police in the immediate aftermath of the fire that he had been playing with matches and had set fire to papers in a cupboard under the stairs.

“The confessions to the police are lacking in the kind of particular detail which would strengthen their credibility,” he said.

Mr Barnes added: “Where the confessions did not marry up with the information known to the police, [Tredget] made further confessions correcting his first account and confirming the police information.”

The case before Lord Justice Fulford, Mr Justice Hilliard and Peter Tredget, formerly known as Bruce Lee and Peter Dinsdale is due to last two weeks, with the Crown’s arguments to come.