Shadow home secretary Diane Abbott has said she no longer opposed the security services as she insisted her time as a graduate civil servant would prepare her for becoming home secretary.
Ms Abbott also tried to distance herself from claims she supported the IRA in the 1980s, saying: "I don't have the same hairstyle, I don't have the same views."
It came as Labour pledged to recruit 1,000 more staff at security and intelligence agencies MI5, MI6 and GCHQ to step up efforts to prevent terrorism.
Ms Abbott was challenged on her views after it emerged she had signed a parliamentary motion calling for an end to "conspiratorial groups" in 1989.
She told the BBC's Andrew Marr Show: "At that time, I and a lot of people felt MI5 needed reforming.
"It has since been reformed and of course I would not call for its abolition now."
Pressed on the issue, she said: "That MI5 has gone. It's been reformed, it's a different MI5 and that's why so many of us are able to support it now."
She defended voting against "counter-productive" counter terror legislation, which was also opposed by many senior Conservatives.
Asked about her views on the IRA in the 1980s, she said: "It was 34 years ago, I had a rather splendid afro at the time. I don't have the same hairstyle, I don't have the same views.
"It was 34 years on. The hairstyle is gone, some of the views are gone."
Ms Abbott insisted that she had worked as a graduate trainee in the Home Office so she was qualified to take on the role, which would make her the first black person to hold one of the most senior ministerial positions.
She said: "First of all, I think there's something to be said for a home secretary who has actually worked in the Home Office.
"I worked in the Home Office for nearly three years as a graduate trainee and I know how it works from the inside."
Ms Abbott, who has represented Hackney North for 30 years, said her experience working in diverse communities would help her in the role.
Home Secretary Amber Rudd shot back at Ms Abbott's comments, telling the Andrew Marr Show: "What I would say to Diane Abbott is I have changed my hairstyle a few times in 34 years as well, but I have not changed my view about how we keep the British public safe."
In a wide-ranging interview, Ms Abbott was quizzed on her views on security issues including her bid to prevent innocent children's DNA being stored in a database and working with tech companies on encryption in messages.
On encryption, she said: "I think the problem with a lot of these companies is they are American companies and they feel very strongly about the right to free speech and so on, but we do have to work with them to allow us to access some of these messages.
"There is an issue about end-to-end encryption, we have to work with them, and if they are not willing to cooperate then we do have to consider what further action we could take."
Labour's plans to beef up numbers of security and intelligence staff would not require additional funding, because the Government has already put money aside to pay for it.
The party has also pledged to hire 10,000 more police officers, 3,000 more firefighters, 3,000 more prison officers and 500 more border guards in its manifesto.
Labour leader Jeremy Corbyn, asked if Ms Abbott's hairstyle comments trivialised the IRA, told ITV's Peston On Sunday: "Diane's hairstyle is a matter for Diane."
Pressed on the issue, Mr Corbyn said: "We learnt, all of us, a lot from the whole experience of Northern Ireland.
"Remember what it was like... in the late 70s and early 80s, the military presence all over Northern Ireland, the huge divide between communities, the lack of any communication between communities, the idea that there'd be a military solution when we knew there wouldn't be.
"I remember arguing with many people in parliament and when Ian Paisley was thrown out of parliament for accusing the prime minister of talking to the republicans, which she denied she was and it turned out she probably was, I actually defended him on being thrown out of parliament."
Asked if Ms Abbott would be his home secretary, Mr Corbyn appeared to misspeak as he replied: "Diane is our home affairs spokesperson and I'm looking to appoint our shadow cabinet."