After grand dinners at Chequers, the UK prime ministers’ countryside retreat, Theresa May often used to ask her driver to take her 45 minutes across the Buckinghamshire countryside to her home in Maidenhead, rather than staying overnight.

Even as prime minister, May maintained a devotion to her constituency that sometimes baffled aides but encapsulated the contradictions at the heart of one of Britain’s most successful but hard-to-define politicians.

And so it was unsurprising that when Britain’s second female prime minister and one of its longest-serving home secretaries announced her retirement from parliament after 27 years, she chose to do so in her local paper.

“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,” May wrote in the Maidenhead Advertiser.

May was prime minister for three years and will be remembered in large part for her decision to call a snap election in 2017 in an attempt to secure a parliamentary majority, only to lose seats and ultimately, her authority over her party.

Her turbulent years in Downing Street after that election were plagued by party in-fighting as she tried to find a way to deliver a Brexit agreement that would placate both the hard-right and the centrist factions in her party.

She appeared to have succeeded in 2018, when she secured the backing of her cabinet – ironically at Chequers – for a Brexit deal that would have given Britain continued access to the single market for goods. That began to fall apart within days, however, when David Davis, her Brexit secretary, resigned, closely followed by Boris Johnson, who succeeded her in No 10.

May staggered on for almost another year, but stood down after a series of parliamentary defeats on her Brexit deal that confirmed she had lost the support of her party and the Commons as a whole.

Some argue that May’s inability to persuade her party to back her Brexit agreement was a result of her awkward style of personal interaction. She disliked the backslapping nature of the Commons tea rooms, hated small talk and deliberately shunned parliamentary gossip. John Crace, the Guardian’s sketch writer, called her the “Maybot”.

Those close to her, however, insist that in private she could be warm and sensitive, but that she put up a barrier in public in part to counteract perceptions of weakness as one of Britain’s highest-profile female politicians.

Having become involved in Conservative student politics at Oxford, May entered parliament in 1997 as the first ever MP for the newly created seat of Maidenhead. She came to public prominence five years later when as party chair she positioned herself as one of its leading modernisers, warning in her conference speech that the Tories were becoming seen as “the nasty party”.

Her position within the party made her a natural ally of David Cameron, who made her home secretary after winning the 2010 election. She held the post for more than six years until succeeding Cameron as party leader, making her the longest-serving home secretary for 60 years and one of very few who have emerged from the department with their political reputation enhanced.

As home secretary, May championed a range of initiatives to correct what she saw as social injustices, including curtailing police powers to “stop and search”, spearheading efforts to tackle modern slavery and reversing much of Labour’s hard-line antisocial behaviour policies.

Much of that, however, was overshadowed by her uncompromising approach to immigration.

She oversaw the “hostile environment” approach to asylum, which attempted to make it as hard as possible for arrivals to secure refugee status. The policy was blamed in part for the Windrush scandal, in which dozens of people who had lived in Britain for decades were wrongly detained and even deported from the UK.

She was also blamed for the government’s advertising campaign in which vans drove around London emblazoned with the warning: “In the UK illegally? Go home or face arrest.” The vans were criticised by Labour as racist and even by the Ukip leader, Nigel Farage, as “unpleasant”.

To her supporters, her hardline stance on immigration coupled with an interest in social justice in other areas, made her the ideal candidate to replace Cameron when he stood down after the Brexit referendum. Although she had championed the remain cause, May was seen as one of the few figures who could unite her fractious party, especially after Johnson’s leadership bid imploded early in the campaign.

Her critics, however, say that her lack of a clear ideological programme for government was her undoing.

After calling the election in 2017, she watched a commanding poll lead evaporate as she fluctuated between presenting herself as a continuity candidate and a headstrong reformer. The campaign unravelled when she was forced to abandon a controversial signature pledge to reform social care, only to insist as she did so that “nothing has changed”.

Unusually for an outgoing prime minister, May remained as an active backbencher for several years after leaving Downing Street, continuing to fight for causes such as combating modern slavery and human trafficking. She told the Maidenhead Advertiser on Friday she wanted to devote her post-political life to those causes.

Her decision will be seen in the light of polls showing her party is heading for a landslide defeat at this year’s election. She joins dozens of other Tories also stepping down from their seats before this year’s elections.

But where other outgoing Conservative MPs are already looking for lucrative and prominent jobs in the City, May is likely to be one of the few to use her exit from parliament to spend more time in her constituency. Gavin Barwell, her former chief of staff, once said: “I don’t think there has been a prime minister in modern British political history who has been as devoted a constituency MP.”

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