The new law will free and compensate deputy postmasters who were victims of what has been called the UK’s most widespread miscarriage of justice.
Hundreds were wrongly prosecuted after faulty software said money was missing from post office branch accounts.
The next phase of the public inquiry into what went wrong begins on Tuesday.
What is the Post Office Horizon scandal?
More than 900 deputy postmasters have been prosecuted for theft due to inaccurate information from a computer system called Horizont.
The post itself took many cases to court, prosecuting 700 people between 1999 and 2015.
A further 283 cases were brought by other bodies, including the Crown Prosecution Service (CPS).
Many went to prison for false accounting and theft. Many have failed financially.
What is the public inquiry of Postanski Horizont?
It resumes on Tuesday April 9 and is expected to last several weeks, with campaigner Alan Bates and former Post Office chief executive Paula Vennells among those due to give evidence during this stage.
Politicians who were in charge of supervising the Post Office will also appear.
More about the scandal in the Post Office
What is the Fujitsu Horizon system?
It was introduced by the Post Office in 1999.
Subpostmen were quick to complain of system faults after he falsely reported defects – often to the tune of thousands of pounds.
What was the effect on post office staff?
Many former deputy chiefs say that the scandal ruined their lives.
Some used their own money to cover non-existent shortfalls because their contracts said they were responsible for unexplained losses. Many faced bankruptcy or lost their livelihoods.
Marriages have broken up, and some families believe the stress has led to serious health problems, addictions, and even premature death.
Victims of the Post Office scandal tell their own stories about how they were accused of crime.
What does the state do for the victims?
Prime Minister Rishi Sunak told MPs: “We will make sure the truth comes out.”
The law, which applies to sentencing in England and Wales, is expected to free most victims by the end of July.
Convictions will be automatically overturned if:
- processed by the post office or CPS
- for criminal offenses committed in connection with postal operations from 1996 to 2018
- for relevant criminal offenses such as theft, fraud and false accounting
- against the post office assistant, his employees, officers, family members or direct employees of the post office working in the post office that used the Horizont system software
Affected assistant postmasters will receive an interim payment or may instead accept a fixed and final offer of £600,000.
Downing Street has previously said it will work with Scotland and Northern Ireland to ensure that people wrongly accused in those countries are also freed.
What are the other compensation systems for Horizon?
Post Office Minister Kevin Hollinrake previously said the government had budgeted £1bn for compensation.
More than 4,000 people were said to be eligible, under three schemes:
- Group Court Order (GLO) scheme. is for 555 former postmasters (excluding those with criminal convictions) who won a class action lawsuit but received relatively small payouts after court costs. They will now be offered £75,000, but many are expected to ask for more
- Scheme of overturned convictions it is offering those who qualify a quick settlement of £600,000 or the chance to negotiate a higher payment. All are entitled to an “interim” payment of £163,000
- Horizon Shortfall Scheme is for deputy postmasters who have not been convicted, or part of a GLO court case, but who believe they have experienced shortfalls due to Horizon. This group will be offered a fixed payment of £75,000
Professor Chris Hodges, chairman of the independent advisory board Horizon Compensation Advisory, told the BBC that some individual compensation claims were “in excess of more than a million pounds”.