Andrew Ager was involved in 20 previous trials and up to 50 police investigations into allegations of fraudulent carbon credit selling.

The collapse of the case, also partly due to disclosure failings, could see a review of all prosecutions in the past eight years brought by the City of London Police.

Judge Nicholas Loraine-Smith recorded eight verdicts of not guilty against eight men accused of defrauding 72 investors of £3.5 million.

He told jurors the decision “may be of importance in similar cases involving Mr Ager which have taken place in the past and are due to take place in the future”.

Mr Ager admitted he had no relevant academic qualifications, under cross-examination, and while he said he took three A-levels, he could not remember if he had passed any.

Judge Loraine-Smith said that while Mr Ager “knows a lot about the carbon credit market” he “has little if any understanding of the duties of disclosure and nobody from the police or the CPS seems to have taken the time to explain them to him”.

He added that prosecutors’ disclosure had been “pretty chaotic and unsatisfactory”.

Furthermore, Mr Ager’s initial expert statement provided to City of London police was “quite obviously a cut and paste” from a statement of a case at the Old Bailey in 2015.

Narita Bahra QC, for one of the defendants, said that the safety of the “convictions in every previous carbon credits prosecution is now in question” since Mr Ager had been repeatedly used by prosecutors to explain to juries that there were no secondary markets in “voluntary emission reduction” carbon credits.

She added: “It is apparent that there are systemic failures within the investigation and disclosure processes at City of London police that are likely to impact upon all prosecutions undertaken in the last eight years.”

Ms Bahra said outside court: “There is a public perception that disclosure failures are limited to offences involving sexual offences. The reality is they are not. The onus should not be put on a good defence team to elicit material which undermines the prosecution.”

A City of London police spokesman said: “The case illustrates the significant change in the way fraud itself has evolved, along with our response in dealing with it. Together with our colleagues in the CPS, we apologise that the evidential and procedural issues in the case have led to its dismissal.

“Since this case started we have been changing how we and others in policing investigate fraud. Undoubtedly there is key learning we will take from this case which we will use going forward to provide a better service to the victims of fraud.”

The CPS said: “We are considering past cases to identify any in which Andrew Ager appeared as an expert witness and will consider any action necessary once these have been fully reviewed. Mr Ager will not be used as an expert witness in any future cases.”