Ms Smith thinks minister should be better trained
Jacqui Smith feared she was not up to being home secretary and wished she had been better trained for the role, she reveals in a magazine interview.
She told Total Politics magazine she had "never run a major organisation" before accepting the job in 2007.
"I hope I did a good job but if I did it was more by luck than by any kind of development of those skills," she adds.
Ms Smith says she quit as home secretary last month over a "horrible" media storm surrounding her expenses.
She said her first reaction on discovering that her husband had claimed for porn films on her expenses was to tell him: "I am going to have to resign".
She adds: "I then had to go into a meeting which was the hardest thing I have ever had to do. However, it was the Friday before the G20 and people said to me - not the prime minister, you understand - that they didn't think the prime minister or the government were going to thank me for resigning just before the G20."
She also speaks of her first weekend as home secretary, in July 2007, when she had to respond to the abortive terror attacks in central London and Glasgow airport.
"I'm not sure I understood, I'm ashamed to say, when I first heard it, quite how serious it was.
"When somebody rings you up and they say 'a car has been found in Haymarket and it seems like it might have been set up to explode', your first reaction is 'oh, that's interesting'. You then think 'well, now I'm home secretary, so I have responsibility for that'.
"The point at which I felt a bit of cold run through my veins was on the Saturday in the office when the Jeep ran into Glasgow Airport."
She describes the way ministers are moved from one government job to another in Cabinet reshuffles as "pretty dysfunctional in the way that it works" but adds that it is "not just this government".
She says: "I think we should have been better trained. I think there should be more induction.
"There's more now than when I started as a minister but it's still not enough. I think there should be more emphasis given to supporting ministers more generally in terms of developing the skills needed to lead big departments, for example."
Asked if she worried that she was not up to the job, she tells Total Politics: "Well, every single time that I was appointed to a ministerial job I thought that."
She said she "didn't sleep for a week in 1999 when I got my first ministerial job".
Ms Smith, who was the first woman to hold the job of home secretary, is not the first minister to express doubts about their ability to do the job.
Former teacher Estelle Morris quit as education secretary in 2002 after admitting she was not up to the job and Margaret Beckett, despite years of ministerial experience, confessed in May 2006 after taking part in talks about Iran's nuclear ambitions at the UN that she was "flying by the seat of her pants" in her new role as foreign secretary.
There has been criticism of the way in which ministers are parachuted into departments, often without any prior knowledge or experience of the policy area, and expected to manage huge bureaucracies and multi-billion pound budgets.
Ms Smith tells Total Politics that she wanted to improve the system of spotting future ministers on the back benches and training them up for specific roles when she was Labour's chief whip, the job she held before becoming home secretary.
"It was one of the things I wanted to develop and we were never able to do that, but I think you need to acknowledge that you are managing your biggest asset, people, and you need to keep replenishing talent," se says.
She also describes being at the centre of a media storm over her expenses as "horrible" and says that if it had not happened she would not have resigned as home secretary.
On criticism of nominating her sister's London home as her main home for expenses purposes, she says: "I thought it was strange that you could have a main home that wasn't where your family lived," but stresses that she had acted on advice from the Commons Fees Office and was confident she would be cleared by the Parliamentary Standards Commissioner.
Asked what the most romantic thing she has ever done, she replies: "Probably not making my husband sleep on the sofa in the last six months."