Actress Brenda Blethyn, who plays shambolic, sharp, brilliant Detective Chief Inspector Vera Stanhope, surprised author/creator Ann Cleeves by revealing to her the date of Vera's birthday – 21 April. 

"I'd never though of that," laughs Cleeves. 

Indeed, nowhere in any of Cleeves's seven Vera books is her heroine's birthdate mentioned. But it's all part of Blethyn's attention to detail and her actorly need for a full backstory for her characters.  

"I think it's because she's worked with [director] Mike Leigh. It's all about developing characters, and knowing things about the character that nobody else knows, and which might never come up on screen." 

Brenda Blethyn's Vera Stanhope arrived on ITV in 2011 in a first series of adaptations (the fifth starts tonight) that were to cement her as a comfortable, witty, straight-talking Geordie favourite, with ratings routinely hovering around seven million. 

But Vera had been born on the page in 1999 in Cleeves's novel The Crow Trap. Her arrival, as she burst through a set of church doors to interrupt the funeral of a murder victim, came out of the blue for her creator: "I was stuck on The Crow Trap. It was never going to have a detective in it; it was just going to be about three women working on an environmental survey right up in the hills of Northumberland. 

"It was always going to be a crime novel, but in a Minette Walters, psychological suspense way. I'd written the first three parts and couldn't think what i was going to do with the rest of it." 

So Cleeves, a former probation officer and bird observatory cook, fell back on the cast-iron, hard-boiled advice of the great Raymond Chandler, who said: "If you are stuck with a book, have a guy burst through a door with a gun." Says Cleeves; "I don't do guns, of course, but I was writing this funeral scene and everything had started and the door burst open and there she was, like a bag lady instead of a detective. And I had the name, too." 

Thus, fully formed Vera Stanhope (named after a County Durham village) was born. through if you read Cleeves's first description of her, then look at Blethyn's Vera, you might pause: "She was a large woman, big bones amply covered, a bulbous nose, man-sized feet…Her face was blotched and pitted."