The head of the organisation that investigates alleged miscarriages of justice has ordered an urgent review of cases where DNA evidence is involved to find whether there are long-term prisoners whose innocence could now be scientifically proved.

The decision comes as one of the country's leading civil rights lawyers claims that there are now as many miscarriage of justice victims behind bars as there were in the 70s and 80s.

Richard Foster, the chair of the Criminal Cases Review Commission (CCRC), told the Guardian that developments in the gathering of scientific evidence have implications for cases dating back many years. He has asked the Crown Prosecution Service to review all such cases.

"Progress in science means you are able to go back and revisit cases ? Sean Hodgson [released earlier this year having served 27 years for murder after his innocence was proved through DNA testing] is a very good example of that," said Foster, "But scientific understanding and certainty can actually shift ? in cot deaths, for example ? and you can also get the issue of the correct understanding of scientific evidence. You need to be sure it's been explained properly to the jury."

Considering whether there are other Sean Hodgsons in the prison system, he said: "We have started a review of our cases to check that out and I have written to Keir Starmer [the director of public prosecutions] asking him to check."

Foster was speaking on the eve of the launch of a new series on the Guardian's website, Justice on Trial, which will look at alleged miscarriages of justice.

He also said he wanted to reach the many prisoners who may be illiterate, inarticulate or with learning difficulties and who may be unaware of how to claim their innocence. "What we know about most people in prison is that they have quite limited education. Many of them can't read or write," he said. Currently, the CCRC requires prisoners to write to them, something many of them may be unable to do. "We also know that the prisons are under considerable pressure," Foster added, "so I want to investigate whether there are ways to make it easier for people who want to approach us to do so."

Foster believes there may be ­others who, like Sean Hodgson, confessed to crimes they did not commit. "We are understanding better that you do get people who, for psychological reasons, confess to things they didn't do. That has just reinforced us in the view that, if you've got a case that turns largely on confession evidence, you've got to look very carefully at it."

The number of applications to the CCRC, which has the power to refer cases back to the court of appeal, remains fairly constant at about 1,000 a year. Of these, only 2.7% were successful last year, the lowest proportion ever. Foster said that was "a blip" and the figure this year is 4.1%.

Campbell Malone, the lawyer whose work largely led to the release of Stefan Kiszko, said he believed there were a large number of innocent people in prison. "I believe we have a government that is positively hostile to the notion of miscarriages of justice," he said. "It would seem to be of the view that it would be better for the odd person to spend their life in prison for a crime they did not commit than to have the inconvenience of it being exposed." He added that there were "just as many" such cases now as in the 70s and 80s.

The cases that first prompted serious concern involved the Birmingham six and the Guildford four, both during a period when the IRA was active in Britain. Foster said there were similar concerns today. "Where there is intense pressure ? public, political pressure ? in a particular case and around terror, there is always the risk that safeguards that should be in place won't be applied as they should be," he said.

"You have always got to pause if someone continues to say they're innocent, either when they're in prison or, more pointedly, if they're in prison and ruling themselves out of early release because they're not acknowledging their guilt. I think any sensible person is going to pause on that and say ? well, why?"

Foster said he did have "3am moments" as to whether one of the 95% of applications that are screened out and not reinvestigated by the CCRC might be a miscarriage of justice. "I worry about that ? and anybody who works in criminal justice who doesn't ought to think about whether they made the right choice of career."