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Sir David Calvert-Smith, 79, who reviewed scores of appeals for the Post Office, said that in at least 12 convictions, judges ought to have “probed” the prosecution case “more deeply”.

Sir David headed up the Crown Prosecution Service for five years until 2003, when he became a judge in the High Court for seven years.

In 2021, the Post Office instructed him, along with Brian Altman KC, to review 42 convictions before they went to the Court of Appeal.

Thirty-one of the convictions were quashed on appeal.

Speaking at a Bar Council conference in London, Sir David addressed the question of whether some judges in the Crown Court who heard private prosecutions brought by the Post Office had failed subpostmasters.

“That is certainly true in as many as a dozen of the cases I read when I went through them,” he said.

He added: “I thought surely a judge would have probed a bit more deeply rather than thinking ‘I’ve got a full list and I want to get on with my next case’.”

It has been noted that in some cases judges refused repeated applications from the defence over the faulty nature of the Horizon system.