The film, starring Australian Naomi Watts as the much-loved British icon, took less than £600,000 in its opening weekend, barely scraping into the top five.
Diana failed to match the sales figures of its major competitors and was even outsold by About Time, a romantic comedy which has been showing in UK cinemas for three weeks.
Last week’s number two, motor racing drama Rush, has overtaken Insidious: Chapter 2 to slip into the top spot with sales of £1.2m, compared with the horror sequel’s total of £1m.
There is no movement at number three, with White House Down taking £700,000, and About Time (£700,000) is also a non-mover at four, with Diana bringing up the rear.
The royal biopic was met with a mixed reaction from critics when it previewed earlier this month.