"What is different with this novel is that with war, you don't have any inherently bad characters," he says. "That's the main reason I wanted to write about war, because you can have a situation where all the characters are really good people and they screw up because of their own personal flaws and not because they're inherently evil. The war itself is evil and that gives me the luxury of a cast of characters who are all good people, but you still have a story to tell."
Everyone Brave Is Forgiven is also the 42-year-old's most personal work to date, drawing heavily on his own family background, using his maternal grandfather - who served in Malta and North Africa - and grandmother - a school teacher in London during the Blitz - as models for Alistair and Mary respectively. However, he says everything is made up, including the dialogue and plot, with the characters being very close in "their hearts" to his grandparents.
"So it all comes from these people, who were a real part of my life when I was growing up, although I never really talked to them about it until the last three or four years of my grandfather's life, as he wasn't ready to talk about it until then."
Crucially, the novel spans a three-year period, beginning with the outbreak of the war in September 1939 and building up to June 1942 with United States forces having finally joined the growing global conflict. While they entered the war after the bombing of Pearl Harbour in December 1941, US troops didn't arrive in Britain until early to mid-1942.
"At which point, everyone breathed a huge sigh of relief, as everyone thought that if we do lose the war now, it will be because the whole world has lost the war and that would have been very unlikely," Cleave says.
"But before 1942, there was a real uncertainty about who was actually going to win and that's where the bravery comes from because it's so easy to look back afterwards already knowing the result."
It is not US soldiers but rather some of its touring performers who provide the novel with its most intriguing subplot as Helen forms a special bond with Zachary, the young son of a visiting African-American entertainer.
"I had my family story and an incredible amount of detail about what it was like to live in London during the Blitz, and the siege of Malta where the book is also set, but what I didn't have is an original angle," recalls Cleave.
"With World War II, you're stepping into territory that has been re-trodden and re-trodden, so you'd better have a new story to tell. I kept looking and looking, and in the end it was hiding in plain sight. I was looking through hundreds of photos of children who had been evacuated from London at the start of the Blitz - and they were all white."
While he describes the constant abuse Zachary and the novel's other black characters receive as "jaw-droppingly racist", Everyone Brave Is Forgiven's preoccupation with race brings to mind The Other Hand.
The tale of the unlikely friendship between a Nigerian asylum-seeker and an English magazine editor, Cleave's second novel now seems particularly timely after the Syrian refugee crisis that has gripped Europe during the past 12 months.
"I'm really obsessed with migration, as it's the big story of our age, and it doesn't look like stopping anytime soon," says Cleave. "People were laughing at me but when The Other Hand first came out in 2008, I kept saying that this problem is only going to get bigger. So we're either going to have to put up 100ft high barb wire fences around our nation or we're going to have to come to some accommodation with the idea that you don't have to be white to live here."
Cleave certainly has form when it comes to being prophetic. The grim account of a mother dealing with the death of both her husband and child in a terrorist atrocity at a football stadium, Incendiary was fatefully published on July 7, 2005, the same day of the London Tube and bus bombings. While he admits he received "a lot of flak for writing that novel", it now feels even prescient after extremists targeted the Stade de France during the terror attacks in Paris in November.
"There's a kind of sympathetic magic that happens where it's like 'if you wrote about it, then you must have caused it'. If enough people believe that, then you start wondering whether they might have a point," says Cleave. "So I took myself off and had a real word with myself. 'Those people are crazy, not you, as you're writing about the real flashpoints in your society and that's the only thing a serious writer should be writing about, full stop.'"
