Tim Sullivan is an experienced screenwriter whose work ranges from the film Jack and Sarah to My Little Pony.

While working at Granada in the '90s he directed The Casebook of Sherlock Holmes, and wrote the crime drama Maigret.

"I've always liked good crime fiction from Chandler to Hammett," says the Islington resident, who created his own detective stories during lockdown, and self published them.

It led to a publishing deal for his crime thrillers featuring idiosyncratic Detective Sergeant George Cross.

"At the beginning of lockdown everything slowed up on the film front," said the 64-year-old. "I thought now's the chance if you are going to do it."

Sullivan's police procedurals are set in Bristol where his parents hail from. Cross has Asperger's and champions the outsider, the voiceless and the dispossessed in books such as The Dentist, which sees the body of a homeless man found strangled on the Downs, and The Cyclist in which a plastic-wrapped body turns up in a mechanical digger.

"If you look at the great detectives in fiction, most of them are probably on the spectrum," says Sullivan. "I wanted to show the condition in a positive light. People have difficulty working with George, then come to understand that for him things have to be right. He can't settle unless he's got to the bottom of a case. He doesn't have gut instincts, he will only deal with what's in front of him. Even if they find someone that all the evidence points towards, if something unsettles him he will pursue a line of enquiry until he crosses it off."

Islington Gazette: The Patient is Tim Sullivan's third DC Cross thriller and is published by Head of ZeusThe Patient is Tim Sullivan's third DC Cross thriller and is published by Head of Zeus (Image: Supplied)

Sullivan has striven not to treat George's neurodiversity as a "gimmick," and rejected the usual crime "tropes" of a detective with a broken marriage and drink problem.

"With successful detective fiction it's the character at the heart of it, not the crime. People really respond to George and feel for him. That's the key."

Self publishing was a blessed relief after the screenwriter's malaise of waiting for projects to be green lit.

"The problem with being a moderately successful screenwriter is that 80 percent of the work doesn't get produced. I worked for a year on Shrek 4, then a new director came in with a totally different vision, and wrote a really great script for Ron Howard who loved it so much he made someone else's Western."

After teaching himself how to use Facebook and Google to boost his book's profile, Sullivan was thrilled when it gained momentum.

"It was fantastic when the reviews came in. I published and was having responses within days."

American bookseller Barnes&Noble made it one of their top 25, and within months the first two books had 200,000 downloads. Having made back his initial stake and moved into profit, he wasn't sure he needed a publisher.

"Self-publishing used to be a vanity project but now it's a proper business. There are some incredibly successful self-published authors."

He puts his success down to "a really good plot and genuine leads for my police to follow."

"I hate crime novels where there are red herrings for the sake of it. I tend to know who has died and who has done it but I like to discover the plot as I go along. It gives the reader and the character a chance to find out things at the same time."

Sullivan wrote his first short film while at Cambridge University, then met the late, great Derek Jarman who was a "fantastic encourager of young people".

Within weeks he had helped on a screenplay called Neutron and was asked to write a movie for Jarman. While writing it, he got a job as a chauffeur driving Anthony Andrews around Oxford on the set of Brideshead Revisited.

"I would sit in the car all day scribbling. The producer Derek Granger said 'what on earth is your chauffeur doing? Anthony said: 'he's writing a movie for Derek Jarman'. Soon there was a knock on the window and he became a mentor and I did two movies with him."

A Handful of Dust starred Alec Guinness and Judi Dench, while Where Angels Fear to Tread featured Helen Mirren and Helena Bonham Carter. Sullivan describes his film career as a combination of "ambition, luck and drive with a tiny bit of talent thrown in."

"The lows are low but when it's rewarding it's really rewarding. There's nothing like being on a film set with Eileen Atkins reading your words, making way more of them than they deserved."

Atkins was in the Islington-set movie Jack and Sarah alongside Judi Dench, Ian McKellen and Sullivan's daughter Sofia as the toddler raised by Richard E Grant's widower. She was cast during a session in his house involving 20 sets of twins.

"Sofia was walking around and thought it was amazing. The cinematographer was filming me working with the twins and at the end I said 'have we found one?'. He said 'yes'. So Jack and Sara was the most expensive home movie ever."