Former business secretary Sir Vince Cable has told the Horizon IT inquiry he accepts responsibility for oversight of a department during the scandal where “clearly there was a policy failure”.

The ex-Liberal Democrats leader told the probe he “hadn’t the faintest idea” the Post Office was privately prosecuting subpostmasters but recognised Sir Alan Bates’ description of the company as “thugs in suits”.

Sir Vince, who was business secretary between 2010 and 2015, apologised to victims of the Horizon scandal who were “so grievously let down” and said he needed to share “some responsibility for the fact that this happened on our watch”.

He told the probe problems with Horizon “barely came across my desk”, adding: “When they did it was usually in a very uncontroversial way.”

In his witness statement to the inquiry, Sir Vince said: “These abuses occurred under a large number of ministers in Labour, coalition and Conservative governments and we all share some responsibility for the fact that this happened on our watch.

“I accept my share of that responsibility and apologise to the victims for the fact that they were so grievously let down.

“I should add that while the focus of the inquiry is quite properly on the subpostmasters and injury that they have suffered, the dishonesty of Post Office officials has also done harm to trust in official advice without which government cannot properly function.”

Adding to the words in witness statement, Sir Vince said on Thursday: “To be frank, I found it very difficult to pinpoint particular events or decisions that I could have done differently – but simply, as a matter of formal responsibility, this was a state enterprise that came within the remit of my department and I accept the fact that it happened on our watch.

“I know that’s a cliche, but it’s something that ministers have to recognise.”

Counsel to the inquiry Jason Beer asked: “When you say that you accept your share of responsibility, what are you accepting responsibility for?”

Sir Vince replied: “General oversight of the department and this was an area of the department where, clearly, there was a policy failure.”

The ex-Liberal Democrats MP for Twickenham said the Post Office had dealt with MPs in an “arrogant way” when they campaigned against branch closures.

He wrote in his witness statement: “When we came into government, Ed Davey and I agreed based on our experience as constituency MPs that Post Office middle management were, as I described in my 1999 debate, ‘authoritarian’.

“Mr Bates has, I believe, described them as ‘thugs in suits’ and I recognise the description.

“And Post Office dealt with us in an arrogant way when we campaigned against closures.”

Asked to what extent the secretary of state was responsible for oversight of the Post Office’s private prosecutions, Sir Vince said in his statement: “On a practical level, I hadn’t the faintest idea that this was happening.”

Addressing his knowledge of issues with the faulty accounting software, Sir Vince said: “I have attempted to describe events as far as I can recall them, though the fact that they took place so long ago – coupled with the fact that problems with Horizon barely came across my desk – means that my recollection may not be perfect.”

Questioned on why Horizon issues barely came across his desk, Sir Vince told the probe: “I think the general reason is that the officials who were briefing me and the ministers on the subject hadn’t seen it as a particular problem.”

He added: “I think with hindsight, I should have been told at the outset about Horizon and what it was.

“We should have been told people were suggesting there was a risk factor and I should have been told about Mr Bates and the justice group.

“I’d never heard his name until I’d been in the job five years.

“Certainly I wasn’t briefed on them – probably this came down to civil servants making a judgment that because I had a vast area of responsibility and because it was being well handled at a minister level I didn’t need to be told about them.”

More than 700 subpostmasters were prosecuted by the Post Office and handed criminal convictions between 1999 and 2015 as Fujitsu’s faulty Horizon system made it appear as though money was missing at their branches.

Hundreds of subpostmasters are still awaiting full compensation despite the Government announcing that those who have had convictions quashed are eligible for £600,000 payouts.