On the plus side, crime levels fell, the UK avoided a large-scale terrorist attack and in 2013, she successfully deported radical cleric Abu Qatada – something she listed as one of her proudest achievements, along with preventing the extradition to America of computer hacker Gary McKinnon.
However, the Passport Office suffered a near meltdown and she faced constant criticism over the government’s failure to meet its promise to get net migration down to below 100,000 a year.
Despite the fact that she never came close to meeting this target, she has consistently refused to drop it.
Labour MP Yvette Cooper, who went up against her in the Commons as shadow home secretary, told the Guardian:, external “I respect her style – it is steady and serious. She is authoritative in parliament – superficial attacks on her bounce off.
“The flip side is that she is not fleet of foot when crises build, she digs in her heels (remember the Passport Agency crisis in 2014 when the backlog caused hundreds to miss their holidays, and the Border Force crisis in 2011 when border checks were axed).
“And she hides when things go wrong. No interviews, no quotes, nothing to reassure people or to remind people she even exists. It’s helped her survive as home secretary – but if you are prime minister, eventually the buck has to stop.”
There was a bitter public row with cabinet colleague Michael Gove over the best way to combat Islamist extremism, which ended with Mr Gove having to apologise to the prime minister and Mrs May having to sack a long-serving special adviser.
Former Conservative chancellor Ken Clarke also had run-ins with her and was recorded on camera saying that Mrs May was good at her job but a “bloody difficult woman”, a bit like his former boss Mrs Thatcher.
She has rarely opened up about her private life although she revealed in 2013 that she had been diagnosed with type 1 diabetes and would require insulin injections twice a day for the rest of her life – something she says she had come to terms with and which would not affect her career.