Martin Marprelate, an anonymous pseudonym authoring a collection of eight illegal, serialized narratives: “Epistle,” “Epitome,” “Hay Any Work,” “Metaphysical School-points,” “Theses Martinianae,” “Just Censure,” “More Work for Cooper,” and “The Protestation” (1588-1589)
There are multiple candidates for first novel in English partly because of ignorance of earlier works, but largely because the term novel can be defined so as to exclude earlier candidates. (The article for novel contains detailed information on the history of the terms "novel" and "romance" and the bodies of texts they defined in a historical perspective.)
Length
Critics typically require a novel to have a certain length. This would exclude Oroonoko, arguably a novella.
Content and intent
Critics typically require a novel to be wholly original and so exclude retellings such as Le Morte d'Arthur.
Critics typically make a distinction between collections of short stories, even those sharing common themes and settings, and novels per se, which typically has a single protagonist and narrative throughout. This might also lead to the exclusion of Le Morte d'Arthur.
Critics typically distinguish between the romance, which has a heroic protagonist and fantastic elements, and the novel, which attempts to present a realistic story. This would, yet again, exclude Le Morte d'Arthur.
Critics typically distinguish between the allegory (in which characters and events have political, religious or other meanings) and the novel, in which characters and events stand only for themselves, and so exclude The Pilgrim's Progress and A Tale of a Tub.
Critics typically distinguish between the picaresque, made up of a connected sequence of episodes, and the novel, which has unity of structure, and so exclude The Unfortunate Traveller.