Video report by ITV News Meridian's Sarah Saunders
Postmasters and mistresses from across the South East who were convicted of theft, fraud and false accounting have began an attempt to clear their names.
The four-day hearing at the Court of Appeal will consider convictions against 42 former sub-postmasters, which the group claim are unsafe because of failings in the Post Office's Fujitsu-developed Horizon IT system.
The Criminal Cases Review Commission (CCRC) referred their convictions to the Court of Appeal last year, having decided there is "a real possibility" that their convictions are unsafe.
In December 2019, the Post Office settled a group action brought against it by more than 550 claimants, paying out £57.75m without admitting liability.
The Horizon computer system was first installed into Post Offices back in 1999. However, by the early 2000's, money had started disappearing from accounts.
Over the next 15 years, many postmasters and mistresses were charged with fraud and theft, with some jailed.
Pauline Thomson ran the post office in the Kent village of Matfield.
She was accused of stealing from the post office, later arrested and eventually convicted of false accounting.
It is a conviction she hopes will be quashed by the court, after the post office accounting system was discredited.
Pauline says: "I didn't know what to do. It was like looking at someone else figures on the screen, it just didn't match up, I was only a sub-post office, I shouldn't have had all that money.
"I came down and saw two auditors and I told them straight away the cash on the screen would not match the cash in the safe. It was a sub post office it just wouldn't have that."
Jo Hamilton, a former postmistress from South Warnborough, who was wrongly convicted of fraud during the post office scandal, is also one of those bidding to clear her name.
The Post Office has previously said it 'sincerely apologises to postmasters affected by historical events' and has taken 'determined action to provide both redress for the past and fundamental reform for the future'.
The hearing before Lord Justice Holroyde, Mr Justice Picken and Mrs Justice Farbey is expected to conclude on Thursday or Friday, and it is expected that they will give their ruling at a later date.