The scene where Nick the Greek breaks the glass in the coffee table was not in the original script. It was, in fact, an accident that happened during filming and was written in by Guy Ritchie as an afterthought.
Lenny McLean was ill during filming with what he believed was the flu. After filming had ended he was hospitalized and initially told that he had pleurisy. However, tests revealed that he had lung cancer which had metastasized to his brain.
The ending to the film was altered some time after filming had been completed which is why Tom is wearing a woolen cap pulled low down - the actor had grown his hair in the intervening period and did not want to shave it short again. (See also goofs)
When Nick the Greek and Tom are haggling over the price of the stereo, Nick says "All right, all right, keep your Alans on!" The "Alans" in question is cockney rhyming slang, short for Alan Whicker: Alan Whicker=Knickers.
The music that plays just before Hatchet Harry shoots Gary with the antique shotgun is from For a Few Dollars More (1965) (For a Few Dollars More). It's from a pocket watch that Del Indio would play, and when the music stopped he would draw and shoot someone.
The bar that is used as J.D.'s bar in the movie is really called Vic Naylors, it is exactly as it is seen in the film (apart from the sign on the front of course). It is situated in an area of London called Farringdon and is opposite the old Smithfield meat market.
In several scenes "Nick the Greek" is referred to as "Nick the Bubble". This is truncated Cockney rhyming slang; "Bubble and Squeak" = "Greek". In the 1960 Peter Sellers film Two Way Stretch (1960), someone refers to an unseen character "Nick the Bubble".
The film was having trouble finding an American distributor when Trudie Styler called an acquaintance of hers - Tom Cruise. He attended a screening and loved the film. Matthew Vaughn later recalled, "It was hysterical. You had all these mid-level executives sitting there, and Cruise walked in. He saw them all sit up and pay attention, all getting on their phones, and suddenly all these senior executives joined the screening ... At the end, Tom got up in front of everyone and said 'This is the best movie I've seen in years, you guys would be fools not to buy it.'"
Trudie Styler was the one who found the screenplay in the 1990s and was instrumental in getting it made. What she didn't love was the presentation: "It wasn't an easy read," she said. "It was a very long, rambling screenplay with terrible typos, and really poorly presented." Her husband, Sting, appears in the film.
Madonna liked the film's soundtrack so much that she contacted Guy Ritchie and Matthew Vaughn and asked if her label, Maverick, could release the film's soundtrack in the U.S. Ironically, Ritchie said she "wined and dined" them in Hollywood a few times, but that it was Vaughn she was romantically interested in, not him.
Jason Flemyng later claimed to have lost so much money while playing poker with the film's backers in between takes on set that he had to work on the four days of re-shoots the film required for no fee.
Vera Day, who plays Tanya the dealer, bears a striking resemblance to the character of Lady Fingers in the famous film The Cincinnati Kid (1965), a classic about a young card pro who takes on a older foe.
In the starting scene, Bacon says : 'Too late, too late' will be the cry, when the man with the bargains has passed you by. In _Elementary_, Vinnie Jones, delivers a version of Bacon's dialogue, "'Too late, too late' will be the cry, when the lady with the bag passes by" to Sherlock Holmes.
According to Dexter Fletcher, Guy Ritchie had the cast play football and divided them into 5-aside teams based on their characters (the four main lad, plus Sting, the dealers, the villains, etc). The winning team was Hatchet Harry's team, given that they had a professional footballer on their team - Vinnie Jones.
The trivia items below may give away important plot points.
The film's original ending had the four lads walking off with the money, with Big Chris and his son about to follow them to retrieve it. This was changed due to negative test screenings. According to Nick Moran, Guy Ritchie scrambled a new ending on the back of a cigarette packet.
When Big Chris is beating Dog to death with the car door, Vinnie Jones was actually slamming the door into a pile of bricks. Dexter Fletcher recalled that everyone was in stunned terrified silence when the scene was over.