Youngest of the five children of Gordon Ernest Collingridge (1927-2007)^[4] and his wife Irene (born Irene Keeping), Collingridge was born and brought up in Woking, Surrey in England. She read Geography at Hertford College, Oxford, where she earned a first class MA in 1990,^[5] despite contracting viral encephalitis in her second year which caused an almost fatal swelling of her brain.^[6] It was also at Oxford that she met her husband Allan Watt.^[7]

After graduating, Collingridge moved immediately to a career in television, first as a question checker on game shows Wheel of Fortune and Win, Lose or Draw, and then for 14 months as a weathergirl on BBC Scotland.^[6] In the early to mid-1990s she appeared from time to time on BBC television's Gardeners' World. She worked on Spanish public television in 1993 as a co-presenter of "That's English!", an english learning program for spanish people.^[8] She has since worked as a producer and presenter on all five British national terrestrial television channels, as well as BBC national radio.^[5]

In 2000 she quit her job as a television presenter on Tonight with Trevor McDonald to author two biographies, one of 18th-century explorer James Cook and one of Celtic warrior queen Boudica.^[7] During her research for the former, she discovered she shared ancestry with controversial Australian writer and illustrator George Collingridge, who asserted in 1895 that Australia was discovered by the Portuguese.^[7][9][10]

She has described her very early interest in feminism in the introduction to her book on Boudica in 2005: "What started as a strong-willed desire for independence became a fully-fledged, bra-burning (if only I had been old enough to wear one) mentality... Certainly, I cannot remember a time when I wasn't acutely aware of the inherently political nature of woman's position in society and – much to my father's disgust and my now extreme embarrassment – by the grand old age of twelve, I would proudly read Cosmopolitan magazine and proclaim myself a feminist!"^[11]

She returned to television in 2007 as writer and narrator of the four-part miniseries Captain Cook: Obsession and Discovery.^[12]

Collingridge has lived in Scotland since 1989, and resides in a converted farmhouse on the shore of Castle Semple Loch near Lochwinnoch with her husband Alan Watt, and sons Archie, Angus, Finn and Dougal.^[6][7][13] In 2017 she completed her PhD in historical cartography at the University of Glasgow, having worked as a broadcaster for BBC Radio Scotland's Buried Treasure and BBC Radio 4's Making History whilst studying.^{[1][5][6][14]}

• Cook: Obsession and Betrayal in the New World (2002), Ebury Press, ISBN 0-09-187913-2
• Boudica (2005), Ebury Press, ISBN 0-09-189819-6