Former Prime Minister Theresa May has announced she will stand down as an MP at the next general election.
Mrs May, who led the country in the wake of the Brexit referendum, has represented Maidenhead in Berkshire for 27 years.
She said the "difficult decision" to leave the seat would enable her to spend more time on "causes close to my heart".
She is one of 64 MPs elected as Conservatives set to quit Parliament.
Mrs May, Conservative PM from 2016 to 2019, said causes such as tackling modern slavery were taking an "increasing amount" of her time.
The next general election must take place by January 2025, but is widely expected to be held later this year.
In the statement to her local paper, the Maidenhead Advertiser, Mrs May said she remained supportive of Rishi Sunak and would be campaigning for a Conservative victory in Maidenhead, the safe Tory seat she has represented since 1997.
She was re-elected at the last election with a 18,846 majority in the seat, which has not been affected by a review of constituency boundaries.
Mrs May, 67, became prime minister in July 2016 after the resignation of David Cameron following the Brexit referendum. She had been home secretary for six years and was a chief architect of the so-called "hostile environment" for immigrants, which led to "go home" vans being sent into areas with large migrant communities.
Her three years in Downing Street were dogged by the Brexit aftermath. Mrs May, who backed remaining in the European Union, came up against strong opposition within the Tory party over her attempts to secure a deal with Brussels.
A snap election in 2017 saw the Conservatives lose their majority in the House of Commons, which some blamed on her manifesto pledge to raise billions of pounds for social care - dubbed a "dementia tax" by critics. She remained in No 10 after striking a deal with Northern Ireland's Democratic Unionist Party.
'Follow her example'
At the Conservative Party conference months later, Mrs May's speech suffered several setbacks: she struggled with a coughing fit, was presented with a P45 by a protester, while letters fell off the wall behind her as she spoke.
Her leadership style was often described by critics as "robotic" - something she answered with a dance to Abba's Dancing Queen before her speech at the party conference in 2018, which became known as the "Maybot".
Tory peer Lord Barwell, who served as Mrs May's Downing Street chief of staff after he lost his Commons seat in 2017, said Mrs May would be missed by Parliament and her constituents.
He said he hoped future PMs would "follow her example" by remaining in Parliament after leaving No 10, adding she had made a "number of important contributions" as a backbencher.
Eventually, opposition to her proposed Brexit deal led to Conservative MPs holding a confidence vote in her leadership, and although she survived, her authority was diminished and she announced her resignation in a tearful speech five months later.
A visibly upset Mrs May ended her time at the head of government by stating she had "enormous and enduring gratitude to have had the opportunity to serve the country I love."
She went to the backbenches from where she was a vocal critic of her successor Boris Johnson before he left Downing Street in 2022 following a mass revolt by ministers over his leadership.
Mrs May's announcement brings to 95 the total number of MPs who say they will be standing down at the next election.
The list includes former ministers Matt Hancock, Dominic Raab, Ben Wallace, Sajid Javid, Kwasi Kwarteng and Chris Grayling.
This is already more than the 74 MPs who stood down ahead of the last election in 2019, and the 31 who quit in the run-up to the snap election in 2017.
But it is broadly in line with the 90 who stood down in 2015, while 149 quit before the 2010 election that followed the expenses scandal and saw Labour ejected from power after 13 years.
She said: "Since stepping down as prime minister I have enjoyed being a backbencher again and having more time to work for my constituents and champion causes close to my heart, including most recently launching a Global Commission on Modern Slavery and Human Trafficking.
"These causes have been taking an increasing amount of my time.
"Because of this, after much careful thought and consideration, I have realised that, looking ahead, I would no longer be able to do my job as an MP in the way I believe is right and my constituents deserve.
Mrs May said there was "no greater privilege" than being an MP, and said serving as prime minister and home secretary would "not have been possible" without the people of Maidenhead.
Gareth Davies, a Treasury minister, said he was saddened by the decision. "I think it's very good when former leaders stay in the House of Commons and contribute to debates," he told Sky News.
"She's certainly brought a lot to debates since she's stood down, and so I'm very sad personally, but wish her well and I think she's justified in moving on after 27 years."
He denied that the number of Tories standing down indicated a lack of confidence in the party's prospects. "This is what happens when you approach a new election," he said.
Anneliese Dodds, the shadow secretary of state for women and equalities, said Mrs May's decision was further evidence of a lack of confidence in Mr Sunak.
"I think this really strengthens those calls for change, those calls for a general election," she said.
