Bob the cat taught James Bowen that 'everybody deserves a second chance'

Speaking at the launch of the film based on his book, he said: “Bob bought me a house and allowed me to pay the mortgage on it, so he has been treating me very well.

“He’s my baby boy. It was him following me about and going out with me that made me realise I didn’t want to just exist anymore, I wanted to be a part of society.”

James’s book tells the story of his own life as a homeless busker battling with drug addiction problems in London, until he struck up an extraordinarily close bond with the stray ginger cat he eventually christened Bob.

Dressed in a smart navy suit with Bob sat across his shoulders, he said at the screening event at London’s Curzon Mayfair cinema: “When I got the book deal, that was crazy and now, standing on the red carpet … it’s all been one crazy moment after another since I met this little man.”

He added that Bob, who was not fazed by the flashing cameras and hordes of fans, “takes the attention and the limelight all in his stride, as if it was every day”.

Little Britain star Anthony Head, who plays Nigel Bowen, added that the film highlights the importance of animals and what it means to be “picked” by them.

He said: “If you are lucky enough to be picked by an animal, they can change your life.

“My partner and I have been picked by a number of animals and it’s wonderful.

“I would say to anyone who wants an animal in their lives, then go to a shelter, because there are so many animals like Bob out there in the UK.”

But while James described the movie as a “fun” story and Anthony said it was “lovely, with a good heart”, the family film, released in the run-up to Christmas, confronts the issues of drug addiction and homelessness.

Anthony said: “It’s a really good film to come out at Christmas, to think about the fact that there are other beings that are not as fortunate as us and the subject doesn’t go away, especially now, as the cold sets in and the nights draw in.

“It’s something that we walk past and we don’t really take in, so when you get a feel-good family movie like this, it’s good that it makes you think about that without rubbing your nose in it.

“It’s really, really clever.”

Actor Luke Treadaway, 32, who plays James in the film, said: “The whole experience from the moment I got the script to right now on the red carpet has been so surreal and unique.

“I felt a responsibility to do it right. Researching the medical issues (associated with drug addiction) was the hardest part and I didn’t want to gloss over the reality of that.”

He said the process of creating the film, which involved him sleeping rough in the capital, had influenced his view on homelessness, adding: “It really did open my eyes a lot.

“It doesn’t take a lot to say hello to people, even if you haven’t got any money to give them.

“Say ‘hi’. Remind them and remind yourself that we are all just human beings spinning around in space and we can be kind to each other.”

Paying a special tribute to his fellow feline actor, he added: “Bob was a treat, a great co-star.”

The premiere was also attended by the Duchess of Cambridge, patron of Action On Addiction, which the screening event supported.

The film is officially released in the UK on Friday.