Former Royal Mail chairman Allan Leighton has said the Post Office Horizon IT scandal is 'unbelievable' and 'terrible'.
During Leighton's term, between 2002 and 2009, the Post Office was a subsidiary of Royal Mail.
"It's unbelievable that it's happened and I just wanted to say that I'm sorry that elements of that occurred while at my tenure at the Royal Mail," he said.
In his written statement, Leighton said, "To the best of my recollection and understanding ... I was not made aware of these serious matters".
He said the scandal was a terrible thing for everybody, "particularly the sub-postmasters and sub-postmistresses".
Between 1999 and 2015 hundreds of sub-postmasters were wrongfully convicted based on faulty Post Office Horizon data.
Leighton was told he would have to come back to continue his answers at a later date.
'Should have tried harder'
Former Post Office investigator Jon Longman said he should have tried harder to get data requested on behalf of Seema Misra, who was pregnant when she was sentenced to prison.
Giving evidence to an inquiry, he said cost should not have come into it while granting Misra's repeated requests for data.
Longman told the inquiry he was of the firm belief that the accounting system was "robust".
Chief executive off the hook
The Post Office's chief executive, Nick Read, has been cleared of all misconduct allegations following an investigation.
The Post Office said Read has the backing of the board to continue in his role following the investigation by an external barrister.
The allegations against Read surfaced earlier this year when former Post Office chairman Henry Staunton told a House of Commons select committee that Read was facing allegations made by the Post Office's former human resources director under its 'speak up' policy.
In a statement, the Post Office said that an independent barrister had investigated the complaint against Read and exonerated him of all misconduct allegations.
