I want to read some of the work written by one of the tutors on my writing course but I don't know the title to any of his books and have heard rumours that he writes under a pseudonym. Today in class he told us that in one of the books he'd written a group of vampires get hold, or attempt to get hold, of nukes and use them to create a nuclear winter so they can walk around 24/7 without fear of the sun. Without anything more specific to go on Google hasn't been much help and I can't find any clues anywhere else. My tutor's name is John Sayle if that helps at all.
That description fits the plot of the 1998 Channel 4 series, Ultraviolet.
The final episode reveals that the vampires' plan does not involve enslaving humanity as suspected. Instead, they plan to cause a nuclear winter, providing long-lasting darkness, and completely wiping out the threat of humanity with an engineered plague. Scientific advances made during their experiments will allow them to survive on synthetic blood and reproduce via live birth, eliminating the need for human victims.
The writing is credited to Joe Ahearne
The details don't line up exactly with those posted in the question, but Vampire Winter by Lois Tilton may be the answer. In it, nukes are dropped and a nuclear winter, or eternal twilight, allows the protagonist, a vampire (as well as other vampires) to roam about 24/7 in the post apocalyptic world after the war.