He was 56.

The best-selling writer, who penned both fictional novels and biographies of underworld figures, died on Monday.

Mr McKay grew up in Keith, Banffshire, before his family moved to Glasgow when he was a teenager.

He became a social worker and remained in the profession for 20 years, becoming director of social work with Argyll and Bute Council. He left to become a journalist and later wrote his first book, a collaboration with former gangster Paul Ferris which was published in 2001. Mr McKay had written to Ferris in prison to suggest that he act as a ghost writer for his story, The Ferris Conspiracy.

He went on to write books about gangland bosses Tam McGraw and Arthur Thompson, as well as serial killer Bible John, who terrorised Glasgow in the late 1960s.

In March, Mr McKay told how he had been diagnosed with cancer. At the time, he said: “If I have three months, three years or three decades, I’m living life to the full.

“Cancer doesn’t kill you – it’s giving up that’s deadly. That’s not for me.

“An occasional gangster has taken unkindly to what I’ve written about them and made serious threats.

“I didn’t let those get to me, so why should I let cancer bother me?”