Sir Ed Davey has admitted he 'probably should have said sorry earlier on' for the role he played in the Horizon scandal which saw more than 900 sub-postmasters wrongly prosecuted.
The Liberal Democrat leader had served as post office minister under the coalition government between 2010 and 2012 first apologised to victims earlier this month after the scandal was shoved back in the spotlight following the ITV drama Mr Bates.
But yesterday, Sir Davey, who will give evidence at the public inquiry alongside former Post Office boss Paula Vennells in April, admitted it had taken him too long to speak out.
He told the BBC's Sunday with Laura Kuenssberg: 'I probably should have said sorry earlier on, but it is a huge scandal and our hearts go out to those hundreds of subpostmasters and their families who were treated appallingly.
'The key thing now is to make sure that those exonerations happen quickly, that they get the compensation quickly and that they get to the truth with the inquiry.'
The political leader said he was lie to b the Post Office about the efficacy of their software.
Probed on whether he should have questioned the Post Office's version of events harder, he said: 'I was never asked a question in parliament, actually. It wasn't raised that much with me - Mr Alan Bates did, and that's why I met him.
'There were a few written questions and a few letters, but it wasn't actually until the BBC had a Panorama programme, where they found that insider in Fujitsu who blew the whistle ... and the Panorama programme was aired in August 2015.
'I don't know what ministers at the time knew about that.'
On February 1, Sir Davey said he was 'deeply sorry' for the families who had their lives ruined by 'the greatest miscarriage of justice in our time'.
Writing in the Guardian he said: 'As one of the ministers over the 20 years of this scandal, including my time as minister responsible for postal affairs, I'm sorry I did not see through the Post Office's lies - and that it took me five months to meet Alan Bates, the man who has done so much to uncover it.'
His latest apology comes as former detectives are being drafted in to interrogate a fraud squad - dubbed the 'untouchables' - involved in the wrongful prosecution of hundreds of innocent sub-postmasters during the Horizon scandal.
The new team led by Gary Brooks, former head of major crime at Lancashire Constabulary, will the under-fire Post Office investigate allegations that some detectives used bullying and intimidation tactics.
The former detectives and police officers have been brought in to 'review the quality and effectiveness' of the investigations, which eventually saw more than 900 sub-postmasters wrongly prosecuted between 1999 and 2015.
During the public inquiry into the Horizon scandal concerns have been raised that those investigating 'behaved like mafia gangsters' who were looking to collect 'bounty with threats and lies'.
Former sub-postmasters and sub-postmistresses described feeling intimated by the detectives. Last week during the inquiry, chaired by retired judge Sir Wyn Williams, two wrongly accused postmasters discussed the conduct of two investigators.
Rta Threlfall - who was charged with false accounting and theft of a shortfall of more than £35,000 at her branch - said the 'untouchables' had left her with 'crippling anxiety and depression'.
Lawyer David Enright, who is representing more than 150 postmasters, told The Sunday Times, that three of his clients had already spoken to the team probing the behaviour of detectives, adding that others will be investigated soon.
Four former detectives are reportedly interviewing postmasters and postmistresses involved.
Last week, sacked Post Office chairman Henry Staunton, claimed that 40 investigators who were involved in the Horizon scandal were still employed by he postal service.
A source close to the Post Office, however, reportedly denied this.
Mr Staunton said that the detectives were labelled the 'untouchables' because of the power they wielded. He also alleged that the Post Office chief executive had given them that nickname.
One of the fraud team workers Stephen Bradshaw, however, appeared before the inquiry last month and denied the allegations.
Hundreds of sub-postmasters were wrongly convicted because of faulty accounting software, with the major miscarriage of justice were put back in the spotlight thanks to the ITV drama Mr Bates. It sparked a major public inquiry.
Ms Vennells forfeited her CBE for 'bringing the honours system into disrepute' following her handling of the Horizon crisis, after issuing an apology last month.
She was named on Friday in a list published on the Cabinet Office website as an individual whose honour had been revoked.
A series of other current and former politicians have been or will be questioned by the Post Office Horizon IT Inquiry.
These include Conservative ministers Greg Clark and Kelly Tolhurst, Liberal Democrat politician Sir Vince Cable and Labour shadow cabinet member Pat McFadden.
A Post Office spokesperson said that it is looking into the 'specific allegations' raised during the public inquiry.
They added: 'We are acutely aware of the human cost of the scandal and we are doing all we can to right the wrongs of the past, as far as that is possible.
'We have rightly been criticised for past investigation practices. A team has been recruited solely to review the quality and effectiveness of a number of past investigations arising from the allegations which were made during the Inquiry, to inform current and future practices.
'We hope to share as much information as possible with the former Postmasters in a manner that is compliant with our data protection obligations.'