The number of people affected by the Horizon scandal is a question news editors used to ask me and journalists used to ask themselves when trying to get some kind of handle on scale of this story. This was in the bad old days when the Post Office refused to give out information and no one else had a record of it.

Alan Bates from the Justice for Subpostmasters Alliance always had a perceptive view of the likely scale. In our very first conversation in 2010 he told me the number of people affected could be “the high hundreds, possibly more”. I thought that sounded unlikely.

Computer Weekly’s seminal 2009 article which broke the story featured seven people.

The Welsh-language Taro Naw documentary strand, which broadcast its first investigation the same year, found a further 29.

By the time I did my first investigation for the BBC in 2011, that number had expanded to 55.

Then, in 2013, the Post Office’s own Complaint and Mediation scheme attracted the hitherto unimaginable figure of 150.

In 2017, at the first open hearing of the High Court litigation, we were told that 198 people had signed up as claimants. This included people who had been forced to hand over money and/or been sacked, as well as those who had been prosecuted and convicted.

By the time the group litigation at the High Court began in 2018, there were more than 500 claimants. Of those claimants 74 had been prosecuted and 61 had criminal convictions.

It was only after the claimants had secured their stunning victory at the High Court that the true scale of the scandal became apparent. In April 2020 the Post Office told me it was looking at “around 500 additional cases … which resulted in convictions.”

That was the moment the doors were blown off. We knew there were 500+ people involved in the civil litigation – ie people who had lost money over the scandal, but now the Post Office was fessing up to “around 500” criminal convictions using Horizon evidence.

This admission came at the same time thousands of people were dying of a horrible virus, which rightly dominated the news agenda. I passed the figure to the excellent Tom Witherow at the Daily Mail. He and his editor were equally astounded, but given what was going on in the world, we were lucky it made p27.

On 25 May 2020 we were told the Post Office was “reviewing” 900 prosecutions since 1999, then, in April 2021 we were given the final reckoning – the Post Office believed 736 convictions between 2000 and 2013 might be unsafe . This briefly increased to 738 convictions between 2000 and 2015, but in the last couple of weeks the Post Office has settled on a number of 706.

The number has reduced from 736 “as further information was received during the work” the Post Office is doing to investigate prosecutions based on Horizon IT evidence.

Of these 706 “94… have now been through the appeal Courts” with “71 convictions overturned and 23 dismissed/abandoned/refused permission” (the 72nd conviction which was overturned was a DWP prosecution based on Post Office Horizon IT evidence).

On 11 January the Post Office chief executive told Parliament that 736 convictions were unsafe. If the Post Office is now saying it believes 706 convictions might be unsafe, of which 23 are unlikely to be overturned, we are down to the high six hundreds.

Getting the numbers right matters, as is remembering that every number represents a person and a family being put through hell. The fact these figures are still in “the high hundreds” is almost insane. And that’s before you begin to count the thousands of Postmasters who weren’t prosecuted, but who were still forced to hand over money to cover the holes in their branch accounts. Many of these individuals lost their life savings. Some were sacked anyway, losing their business investment and livelihoods.

I’m rather glad there is going to be a statutory inquiry, so we can at last begin to understand how this happened.

NB – all the unlinked stats above are referenced in my book, which is available below.