Former British prime minister Margaret Thatcher was in hospital Wednesday undergoing precautionary tests as she struggles to recover from a bout of flu, her son and the government said. She was taken to a London hospital Tuesday after contracting the flu last week, which forced her to pull out of a celebration for her 85th birthday. Her son, Mark Thatcher, said his mother was 'in very good spirits', adding that if the tests went well she would be home within days. Prime Minister David Cameron wished Thatcher, Conservative prime minister from 1979 to 1990, a 'speedy recovery.' 'We understand from Lady Thatcher's office that she has been admitted to hospital for precautionary tests following her recent bout of flu,' said a spokesman from Cameron's Downing Street office. 'The prime minister wishes Lady Thatcher a speedy recovery.' Thatcher was given a life peerage under the British honours system which entitles her to sit in the upper house of parliament and gives her the title 'lady'. After visiting his mother at the Cromwell Hospital in west London, her son Mark said: 'She's been recovering quite well but the doctors wanted to bring her into hospital for some routine tests over the next couple of days. 'If they go according to plan she'll be home shortly.' Thatcher withdrew from a reception Thursday to mark her birthday at 10 Downing Street after falling ill with the flu on the same day. Conservative leader Cameron hosted the gathering of around 150 friends and former colleagues to mark Thatcher's birthday, which was on Wednesday. Doctors banned her from public speaking in 2002 following a series of small strokes which aides said left her sometimes confused and with a failing memory. Her daughter Carol wrote in her 2008 memoir that on her worst days Thatcher struggled to finish sentences and would even forget that her loyal husband, businessman Denis, had died in 2003. Dubbed the 'Iron Lady', she was the 20th century's longest-serving occupant of 10 Downing Street. Her premiership polarised opinion: right-wingers hailed her for hauling the country out of the doldrums of the 1970s; the left loathed her for dismantling traditional industry and said her reforms had unpicked the fabric of society. 