Here are some strong contenders, with their arguments:
* "The Romance of the Rose" (c. 1275), by Guillaume de Lorris and Jean de Meun: This long allegorical poem, originally written in French, was later translated into English. It was incredibly popular and influential, though some would argue it doesn't quite fit the modern definition of a novel.
* "Sir Gawain and the Green Knight" (c. 1375): This Middle English alliterative poem, considered one of the greatest works of Arthurian literature, is often cited as a forerunner of the novel.
* "The Canterbury Tales" (c. 1387), by Geoffrey Chaucer: This collection of stories told by a group of pilgrims on their journey to Canterbury is a masterpiece of English literature and arguably the first major work in English to feature a complex narrative and diverse characters.
* "Thomas Malory's Le Morte d'Arthur" (c. 1470): This prose rendition of Arthurian legends, though compiled from earlier sources, is considered by some to be the first major novel in English for its length, complexity, and influence on later writers.
Ultimately, there's no definitive "first" major novel in English. All of these works contributed to the development of the novel form and are important landmarks in English literature.