An expert witness used by the crown in the trial of the 21/7 bombers used "unsound" methods to reach flawed conclusions about whether the mix of materials carried by the accused men amounted to a viable explosive, the court of appeal will hear on Thursday.

Stuart Black prepared evidence that was "not considered to be of sufficient quality" by a former senior scientist at the government-run Forensic Explosives Laboratory, in a report compiled eight years ago, the court will hear.

So concerned was Sean Doyle, who later became chief scientist of the FEL, that he and two colleagues warned superiors and the police that the forensic errors could lead to a miscarriage of justice before the 2007 trial of the plotters.

Lawyers for one of those put on trial will argue in the court of appeal that his conviction should be quashed because of the problems with Dr Black's testimony, after obtaining a copy of a critical report produced by Doyle.

They will say that Manfo Asiedu would never have been convicted if the FEL scientists' doubts about Black's work had been put in front of the jury. Jurors at the original trial into the bomb plot were unable to decide on Asiedu's guilt. Facing a retrial, he pleaded guilty in 2007 to conspiracy to cause explosions.

The lawyers will also point to email and meeting notes between Black, FEL scientists and police officers from the SO15 anti-terrorist branch dated November 2006. These indicate police were aware of faults in Black's analysis but this was not disclosed to the court during the trial.

In dramatic scenes two weeks after the 7/7 bombings which killed 52 people in 2005 the plotters, who were later convicted, were seen fleeing trains and buses after rucksacks they were carrying began popping and fizzing but seemingly failed to detonate. It caused widespread panic and led to a huge security operation in London and indirectly led to the killing of an innocent young Brazilian man, Jean Charles de Menezes, by armed police as he boarded the train at Stockwell tube station.

At the trial four men, Muktar Ibrahim, Yassin Omar, Ramzi Mohammed and Hussain Osman, were also found guilty of conspiracy to murder and sentenced to life in jail in 2007. Central to the plotters' defence at trial was their claim that the bombs they made were deliberately constructed not to explode and were actually a hoax. They claimed that they had planned to carry out a series of fake suicide attacks as part of a protest against the invasion of Iraq. The devices they made were designed, they said, to look as realistic as possible but not to explode.

Black, from Reading university, was called by the prosecution team to testify that the devices were real, but did not explode only because they had only mistakenly failed to get the right ingredients – such as hydrogen peroxide and flour – mixed and concentrated to the correct proportions. An associate professor at Reading's department of archaeology, Black is a specialist in forensic science whose main expertise is dating and sourcing human skeletal remains.

But in a witness statement prepared for the court of appeal hearing, Doyle said that the methods of isotopic and trace element analysis Black used were simply inappropriate for some of the conclusions he had derived.

Black declined to comment.

At the plotters' trial, Asiedu broke ranks and portrayed himself as an unwilling participant. He said that he had dumped one of the devices in a park in Wormwood Scrubs, west London, and later handed himself into police saying that he had backed out of the plot, which he believed was real, at the last minute.

Lawyers for Asiedu will point to a report by Doyle and his FEL colleagues prepared in 2006 which, they say, laid out a series of errors and failings in Black's work. They found his conclusions were "too strong", "not justified" and "not considered to be of sufficient quality" for a criminal trial.

"Dr Black appears to have no quality system in place which would allow sufficient confidence to be placed in his findings and the validity of his results and therefore his conclusions," the report stated. One of Doyle's colleagues at the FEL recommended that the "relevant police and legal authorities" also be alerted, lawyers will reveal.

The lawyers will also point to an email recording a meeting on 13 November 2006 between Black, FEL scientists, and officers from the anti-terrorist branch at which, according to a police note, Black "conceded that one of his findings which plays a significant part in the investigation was unfounded". However, the police note also recorded that "a number of issues were raised by members of the FEL, all of which were resolved to the satisfaction of the parties present".

Four days later, a Met police officer emailed 11 police colleagues about the meeting and said: "In essence some of Stuart's [Dr Black's] work … has been proved to be unsound. Stuart is doing further work that may reassert his original findings but that remains to be seen at this stage." The message added that the "vast majority" of requests to make changes were "minor".

Doyle came forward in 2010 to give sworn statements in support of Asiedu's attempt to have his sentence overturned. But last year a court of appeal judge turned down an earlier appeal of Asiedu's. His reasoning was that at the trial the defence knew that Dr Black had conceded mistakes, apologised and remedied them, that his work had been peer-reviewed and that the defence knew all it needed to know to contest the trial with rigour.

The legal team for the CPS will argue that there was no concealment as Black's notes were made available to the defendants' lawyers. A spokesman for the CPS added: "We will deal with any issues … in court in due course."

The Metropolitan police said: "We await the outcome of the hearing and it would be inappropriate for us to comment further on his claims until the conclusion of this judicial process."

An FEL spokesman said: "Scientists from DSTL's Forensic Explosives Laboratory assisted the Metropolitan police throughout their investigations into the bomb plot of 21 July 2005. Any further questions about this investigation should be addressed to the Metropolitan police."