Dame Margaret Hodge said her decision to step down as Barking MP at the next election was the right one at the right time.
The 77-year-old will have spent 30 years as the town's MP by the time the next election is due in December 2024.
She announced last week that she would not seek re-election and, in an interview with the Post, said the job had been "her life".
"Deciding to cut the umbilical cord was quite difficult.
"But it's the right decision at the right time. I've still got loads of energy. You come into politics to change the world and there's lots of things I still want to make better.
"I'd rather go when I'm on top than go when suddenly I find I haven't got the same energy levels to put in."
The Labour politician was first elected as Barking MP in a by-election in 1994, defeating future prime minister Theresa May among others.
She served under the last Labour government, including her appointment to be the first children's minister in 2003.
But she felt that her biggest achievement during her 27 years was defeating the British National Party.
The BNP had 12 candidates elected to Barking and Dagenham Council in 2006, something Dame Margaret called a protest vote against Labour.
She recalled: "It was a terrible time. It was vicious. There were fights in the street. It was really difficult to go on the doorstep and talk to people because there was hostility.
"They (the BNP) were just trying to engender division and I wanted to promote and foster cohesion.
"We all belong together, we are enriched by each other and I think it was a very important victory for Barking and Dagenham. We absolutely thrashed them."
She defeated a challenge from BNP leader Nick Griffin at the 2010 general election and all of the BNP councillors lost their seats at the local elections in the same year.
But one of her biggest regrets was "letting" the BNP be elected to those council seats.
"I should have picked it up. In 2001, turnout was very low in Barking and Dagenham. I did do a bit of work on the Gascoigne estate, talking to people and it was clear then they were completely fed up with us.
"If I had taken that more seriously, we might have stopped what happened in 2006."
Dame Margaret has been a leading voice in opposing antisemitism, something she has vowed to continue with after leaving parliament.
She recalled receiving a lot of "vile" letters when fighting the BNP but the scale "disappears into oblivion" when compared to what she said she gets on social media for fighting the hard-left on antisemitism.
She said she received 90,000 "mostly hostile" mentions in a two-month period after the Equality and Human Rights Commission published a report in October last year criticising Labour over the issue and its handling of antisemitism complaints.
When asked whether the level of abuse and the fatal stabbing of Sir David Amess had accelerated her decision to step down, Dame Margaret said it had not been a factor.
"I'm not going to shut myself away. I'm an MP, I'm in authority, they're not getting at the real me.
"You have to compartmentalise your professional life as a politician from your personal life."
Dame Margaret said she needs to think about whether she will step back from politics altogether on leaving parliament.
She plans to continue in her role chairing Theatre Royal Stratford East and Royal Holloway, a college at the University of London, as well as campaigning for multinational corporations such as Google and Amazon to pay more tax.
The mother-of-four and grandmother-of-12 also hopes to spend more time enjoying hobbies such as the arts, playing the piano and cooking.
What would her advice be to the person who succeeds her as Barking MP?
"It's a brilliant community in so many ways.
"People accept the lot they are given and it's really important that the MP should lead the fight so that we don't.
"Barking and Dagenham deserves the best and is the best."
Dame Margaret began her political career on Islington Council and spent ten years as leader between 1982 and 1992.
She said she has been "incredibly privileged" by her years of public service.
"I've had the most amazing career and never in my wildest dreams as a young girl ever thought that I'd have this sort of life."
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