One of the biggest mysteries of Hollywood’s golden age is whether James Cagney ever uttered that immortal phrase “Hey, you dirty rat!”.

Growing up and watching his great gangster movies on TV, there is no way that I could have known that one day I would personally meet the great American actor - albeit as an extra in the last major film he made, Ragtime - and witness his response when asked if he had.

It was 1980 and I was working as a film extra. I had joined Central Casting in Wardour Street and had been fortunate enough to be in a few movies.

It could be anything; I appeared in a Star Wars film, a James Bond movie even in Mel Brooks’ History of the World: Part 1 but one day Central Casting told me I had 10 days work on a movie being shot at Shepperton Studios called Ragtime.

I was cast as a Pinkerton private detective circa 1900 New York City. I reported to the theatrical costumiers Berman’s and Nathan’s in Camden Town the following morning in order to be fitted out with an appropriate outfit.

The costume of a ‘Pinkerton’ turned out to be pretty standard US clothes of the period. A white shirt, detachable collar and bow-tie, a very itchy grey suit with braces, black Wingtip shoes (brogues) and a chocolate bowler hat known in the States as a brown Derby.

The first day’s filming took place a week later and us ‘Pinkertons’ in our brown Derbys duly assembled on the studio floor. Milos Forman was the Director (One Flew Over the Cuckoo’s Nest has always been one of my favourite films) and he came over and asked everyone to gather around.

Now, to be honest, when you’re an extra in a movie it’s rare that the Director himself talks to you. You’re usually pushed pillar-to-post by a 3rd assistant and there is normally very little direction given. Not for nothing are you known as ‘background action’.

However there was something a bit odd in Forman’s voice that day. This wasn’t just a normal “stand over there and don’t look at the camera” speech. He started off slowly but we could feel that he was leading up to make some kind of announcement.

“Gentlemen,” he began with his soft Czech accent, “this film is called Ragtime and is based on the novel by E.L. Doctorow, which some of you may have read.” We all looked at each other. Twenty Pinkerton detectives shook their heads in unison. What was this guy on about?

“Oh well, never mind” he continued, “you are a private detective team and it is my pleasure to introduce the actor who is going to play the Police Commissioner Rhinelander Waldo. Gentlemen, he hasn’t made a movie in a long time – it gives me great pleasure to introduce - Mr James Cagney!”

To say you could have heard a pin drop would have been an understatement; you could have heard a pin dropping in Australia. We couldn’t believe it. Jimmy Cagney? Get away! The Hollywood legend? Was he over here? Was he in the room now? Was he still alive?

And then a side door opened and us Pinkertons parted like the Red Sea to let in a little bespectacled man, dressed in his costume of a wing collar and tie, grey waistcoat and a brown Derby hat. Mr James Cagney. One of the world’s greatest film stars and one of the people who put Hollywood on the map.

Our silence was followed by an audible gasp as we took in the moment. A highly respectable slow handclap then went up as he made his way through us.

His face beamed behind his ginger moustache as he repeated over and over “Hi, nice to be here. Thank you, thank you. You’re so kind.” Shaking hands like a politician at the Hustings, you could tell he was extremely moved by our outpouring of affection.

Behind Cagney walked fellow Hollywood veteran and close friend Pat O’Brien (they had made many films together including Angels with Dirty Faces) and the word was that Cagney had only agreed to make Ragtime provided his pal was given a role.

James Cagney, we discovered later, was not a well man but insisted on saying hello to everyone personally. By the time he had reached the end of the Pinkerton collective he turned and tried to quieten down our adoration. It didn’t work. We kept on clapping louder than ever.

Suddenly tears rolled down his face and before long we were all catching our throats and crying a little too. It was the most moving testament to an actor I’ve ever witnessed.

Eventually the applause did stop and we got down to the real reason we were all there – the filming.

Unfortunately, Cagney had all the charisma that he had been born with but his memory had gone. All his lines had to be written up on large idiot boards and those of us at the front of the crowd held them up for him to read.

It didn’t matter though. To us he was still a legend.

We filmed scenes for Ragtime all over the country. From inside Oxford’s Sheldonian Theatre to a perfectly recreated replica of the rooftop restaurant of New York’s Madison Square Garden built at Shepperton Studios (where another legendary Hollywood star Donald O’Connor danced and sang for us).

We often had a chance to chat with the “Yankee Doodle Dandy” Cagney or play cards with Pat O’Brien and they were both ‘Gentlemen’ with perfect manners.

Sadly, Ragtime was to be both Cagney and O’Brien’s final theatrical movie. Pat O’Brien died two years later and Jimmy Cagney three years after that. He was 86.

One day, between takes, one of us brown-hatted Pinkertons asked Cagney whether he had ever actually said “Hey, you dirty rat!” in any of his films.

He goggled at us through his spectacles.

He didn’t know what the hell we were talking about…