Former Post Office boss Paula Vennells apologised for the wrongful convictions of postmasters in one of Britain's biggest miscarriages of justice, but said she didn't believe the scandal had been caused by a conspiracy at the organisation.

Hundreds of postmasters, who ran community post offices, were convicted after a faulty IT system from Japanese company Fujitsu led to shortfalls in their accounts, and the state-run Post Office pursued them despite suggestions that it knew of the problems.

Some spent time in jail, others went bankrupt and saw their marriages and reputations destroyed. Some died before they saw their names cleared.

"I am very, very sorry," Vennells told a long-running inquiry, making her first public comments about the scandal in nearly 10 years.

Vennells, who headed the Post Office from 2012 to 2019, said on Wednesday that her understanding until May 2013 was that no bugs had been found in the Horizon software system.

The 65-year-old ordained priest led the group during a period in which it continued to pursue sub-postmasters despite evidence, according to previous inquiry witnesses, that the software could be remotely accessed.

The public outcry about the scandal was amplified earlier this year when ITV broadcast a drama "Mr Bates vs The Post Office", in which Vennells was a prominent character.

She last spoke publicly about the case in 2015, when she told a committee of lawmakers there was no evidence of a miscarriage of justice.

Later that year, the Post Office halted the prosecutions.

Vennells, who received more than 4.5 million pounds ($5.7 million) in salary and bonuses during her seven-year tenure, stepped down in 2019 before the Post Office agreed to pay 58 million pounds in a settlement with 555 sub-postmasters.