Who is the 21st century British writer known for writing modern love stories?*John Barrington WainLeslie PaulAllan SillitoeIrish Murdoch

In the context of 21st-century British writers known for modern love stories, the most notable figure among the options provided is Iris Murdoch. Although she is more commonly associated with the 20th century, her influence and themes continue to resonate in contemporary literature, especially in the realm of relationships and love. Murdoch's novels often explore the complexities of human relationships, morality, and psychological depth, which are central themes in modern love stories.

The other authors listed, such as John Barrington Wain, Leslie Paul, and Allan Sillitoe, have made significant contributions to British literature, but they do not specifically align with the niche of modern love stories as distinctly as Murdoch does. Therefore, the best answer in this context would be Iris Murdoch.