Who knew what and when?

After months of evidence, the Post Office Inquiry heard from its final witnesses this week.

Closing statements will follow next month before inquiry chair Sir Wyn Williams publishes his final report next year.

Much of the evidence centred around who knew what and when, so what did we learn from the key players? And what questions still need to be answered?

Paula Vennells was the chief executive of the Post Office from 2012 to 2019. Her appearance before the inquiry, over three days in May, was hotly anticipated.

The key questions were: what did she know about problems with Horizon, and when did she find out about them?

In the end, we got plenty of tears, as she appeared to repeatedly wilt under probing questioning, but few concrete answers. There was a great deal she claimed she couldn’t remember, and even more she said she had never been told.

“You are not responsible for everything that happens underneath you. You have to rely on the advice of internal and external experts,” she argued.

A lawyer for the sub-postmasters accused her of living in “a cloud of denial”. The inquiry’s own lead counsel asked sardonically whether she was “the unluckiest CEO in history”.

There were lots of questions about whether she had been more focused on protecting the Post Office brand than its people, with her attitude towards press coverage placed under a harsh spotlight.

We saw scathing text messages from Dame Moya Greene, the former head of Royal Mail, which cast doubt on Ms Vennells’ honesty. But amid all the tears and apologies, there were few certainties.

Yet those three days of awkward testimony, and a 775-page witness statement, will still provide plenty of food for thought for Sir Wyn as he prepares his report.

Few people played a more pivotal role than Gareth Jenkins in the Post Office scandal. The senior engineer from Fujitsu helped build the flawed Horizon system and provided expert evidence in several court cases testifying that the system was robust.

In July 2013 the Post Office received bombshell legal advice that Mr Jenkins was “in plain breach of his duty as an expert witness”, and this put the Post Office “in breach of its duty as a prosecutor”.

After this the Post Office paused its prosecutions and decided to replace Mr Jenkins as an expert witness. Which Fujitsu executives knew about this?

When asked at the inquiry, former Fujitsu chief executive Duncan Tait said he had never recalled being told of any issues with Mr Jenkins.

However, a Post Office briefing from November 2013 seen by the BBC suggests that Post Office executives did plan to raise the issue of Gareth Jenkins with him, and a subsequent meeting had been planned between Fujitsu and the Post Office to discuss finding “an independent expert to give evidence about the Horizon system”.

If Fujitsu executives knew about concerns over Mr Jenkins’ past evidence, it raises serious questions about why Fujitsu used Mr Jenkins in the 2019 Bates v Post Office trial. Although he never appeared as an expert witness, he provided behind-the-scenes technical support and information to other witnesses.

How much did politicians in positions of power know about what was going on at the Post Office? Not enough, most have told the inquiry.

Several said they weren’t given a true picture by the Post Office executives they met with, or by civil servants. Former Minster Jo Swinson told the inquiry she has since found out what was really happening during her time in power and realised it was “actually the opposite of what I was being told”.

New Conservative leader Kemi Badenoch complained that when she was business secretary she was given the “vanilla view of what’s going on” from civil servants.

Another theme that has emerged is that people weren’t in their roles long enough, and weren’t given proper handovers. Ministers would come into their posts without a knowledge of the Horizon issues – and just as they were beginning to grasp them, an election or a reshuffle would intervene and they would leave the role.

One of the barristers representing sub-postmasters pointed to the problems caused by this “revolving door of ministers”, as he listed the eight business secretaries in the last five years alone.

Every politician who came to the inquiry had reasons why they weren’t to blame for not doing more during their time in power.

But they couldn’t claim they were totally oblivious – there were campaigners and MPs pleading with them to push the Post Office for answers on Horizon.

As Jo Swinson said in her evidence: “I have asked myself why did I not push harder?”

The inquiry has also been investigating the here and now. But what needs to change to prevent this scandal from happening again?

Horizon is still in branches. This week, we learned there are 16 bugs in the system right now.

The European boss of Fujitsu said he was “very worried” about any extension to a project that should have been retired long ago. He even refused to confirm if it was able to produce reliable accounts.

However, in an extraordinary admission, Paul Patterson revealed the Post Office contacted him as he was heading into the inquiry room to ask if they could use it for another four years.

Sir Wyn has also been asking witnesses about how the Post Office should be run, and even if it is worth saving at all.

The new boss jumped the gun somewhat by announcing his plans this week. Nigel Railton said they are all about putting sub-postmasters at the “heart” of the business. It could involve job cuts and branch closures.

The problem? One: sub-postmasters have heard this before. Two: money. These plans are dependent on government cash. Replacing Horizon will be particularly expensive.

Post Office bosses say they have had “positive” discussions with the government. But, as the saying goes, talk is cheap.

Kemi Badenoch warned the inquiry that the organisation will always lose out if it has to compete with the NHS or schools for funding.

What the inquiry says about the future could be just as consequential as what it says about the past.

Reporting by Theo Leggett, Nalini Sivathasan, Tom Beal and Peter Ruddick