Ed Davey has accused senior Post Office managers of unleashing a “conspiracy of lies” against successive ministers as he defended – and refused to apologise for – his role in the Horizon scandal. The Liberal Democrat leader, who has been criticised for letting down victims of the miscarriage of justice as postal affairs minister between 2010 and 2012, said the government had “dragged their feet” on overturning convictions and issuing compensation payments. He also questioned why the Tories had awarded the former Post Office chief executive Paula Vennells a CBE in the 2019 new year honours list, even though hundreds of post office operators had launched a group action in the high court two years before. In an interview with the Guardian, the Lib Dem leader said his focus was on getting justice for post office operators who were prosecuted for taking money from their businesses as a result of faulty Post Office software, developed by the Japanese firm Fujitsu. “It’s really important that we get to the bottom of this, that we get the truth, that the people in the Post Office who were perpetrating this conspiracy of lies, that they are held to account,” he said. Davey welcomed Scotland Yard’s decision to look into potential offences in relation to the Post Office’s investigations and prosecutions. But in the face of criticism that he should have done more at the time, he said he had challenged the Post Office for answers but that he and his civil servants were misled. “We were reassured time and again that the Horizon system was working. We were told there weren’t that many postmasters affected. We were just told so many lies,” he said. “We absolutely have to have these people completely exonerated – their convictions must be overturned. The Post Office lied to judges and the courts.” The former minister said he felt “sick to the stomach” about the way he and successive post office ministers had been misled, but stopped short of apologising to victims. “I completely understand their anger. This is an appalling miscarriage of justice. I wish I knew then what I know now,” he said. “I deeply regret that I was lied to on such a scale … I hope they understand that I pushed really hard on the Post Office for answers and I got the same answers time and again. Other ministers did as well.” Davey was the first post office minister to meet Alan Bates, the post office operator who led the campaign, despite advice from officials. “Initially I was told not to, but I insisted when I read some of his letters because I could hear his anger. I took his arguments to the Post Office but I was lied to,” he said. After No 10 said Rishi Sunak would “strongly support” the honours forfeiture committee if it decided to review Vennells’ CBE in light of the scandal, Davey said he was “completely surprised” that she had been awarded one in the first place. “They knew all about this,” he said. “I’d like to know who signed it off. It was a bizarre decision given that this was clearly in the public domain. Imagine how the subpostmasters must have felt when they saw that.” As ministers finally held urgent talks on the issue, he accused the government and the Post Office of “dragging their feet”, adding: “They’re still allowing people to live without compensation, they haven’t overturned their convictions. The case is overwhelming. All these convictions should be quashed.” Lib Dem insiders have accused the Tories of weaponising Davey’s time in the role, rather than focusing on the other 15 post office ministers over the period. However, Davey said he was “not going to start pointing fingers” at other ministers who had also been misled.