Margaret Thatcher's private secretary has become the latest member of the former prime minister's inner circle to label Oscar-tipped biopic The Iron Lady as a work of fantasy.

On Sunday, Meryl Streep's portrayal of Britain's longest serving postwar leader earned her a Golden Globe for best actress in a drama. Streep was revealed as a Bafta nominee this morning, and is seen by many as a clear frontrunner to take the best actress Oscar next month.

But Cynthia Crawford, who has worked for Thatcher since 1978 and still visits her every other week, said scenes in Phyllida Lloyd's film depicting her suffering from dementia in later life were highly inaccurate.

"I can assure you that the domestic scenes, and in fact all the domestic scenes in the film, are just absolutely inconceivable," she told BBC Hereford and Worcester. "They're just not right and totally unrelated to the truth."

Crawford said she was particularly upset by a scene in which Thatcher did not recognise herself on TV. "Never, ever – I've never known her to read anything about herself or watch a programme or interview about herself because she refused to," she said. Other galling segments included a segue in which Thatcher packed up her late husband Dennis' clothes and another in which she bought a pint of milk after apparently giving her minders the slip.

"The dementia scenes are disproportionate to her life and her business and her being prime minister," said Crawford. "I think that's really very sad – Lady Thatcher's policy was you look forward, you don't look back. If they had made the film about the 11-and-a-half years of her life as prime minister it could have been absolutely fantastic."

Crawford, who lives in Worcester, did however praise Streep's performance and ability to capture Thatcher's mannerisms, though she said the US actor had not "quite got the walk". She said she hoped to see Streep win the Academy award next month.

Should that happen, Norman Tebbit, who was a member of Thatcher's cabinet between 1981 and 1987, is unlikely to be applauding on Oscars night. Writing in the Daily Telegraph last year, he said Thatcher "was never, in my experience, the half-hysterical, overemotional, overacting woman portrayed by Meryl Streep".

Thatcher's biographer John Campbell has also criticised The Iron Lady for what he said were serious inaccuracies. "It's oversimplified history and there is too much concentration on her," he told the Telegraph last year. "There is a lot of poetic licence going on, including Meryl's way of talking to colleagues."