A 21-year-old student was named last night as the winner of one of Britain's most lucrative art prizes.

Charlotte Harris, a student at Leeds University, won the National Portrait Gallery's BP Portrait Award for her untitled painting of her 83-year-old grandmother, Doris Davis, who lives in Kent. Ms Harris won £25,000 plus a commission of £3,000 to paint a portrait for the gallery's collection.

Ms Harris, the youngest artist on this year's shortlist of four, is in her final year of a BA course in fine art. The oil on canvas portrait took three months to complete over summer last year.

Sandy Nairne, director of the National Portrait Gallery, described the work as "extraordinary and telling". The winner was announced at a ceremony at the gallery in London's Trafalgar Square.

Ms Harris beat Michael Gaskell, 40, born on Merseyside and now living in Sheffield, who was twice commended in previous competitions. He came second for his painting Noura and won £8,000. Irish-born Graham Flack, 41, who lives in Edinburgh, won the £4,000 third prize for Elliott II and Dean Marsh, 35, a Londoner who was also formerly commended, came fourth with Man With Grey Scarf.