The Clear Sky travel agency has a six digit (should be seven) 0171 phone number. The 0171 code didn't exist until 1995, before that it was 071, and in the 1980's when the scene is set, the code for London was 01.
In two of the London arial shots, three Mercedes Citaro low-floor articulated buses can be clearly seen - which only started production in 1997, and were introduced to London in 2002. Moreover, there were no articulated buses in London at all in 1980, when the movie is set.
In the opening scenes Jason Stratham is using the Beretta 92F handgun first manufactured in 1992 and the film is set in 1980. However, the Beretta 92S was available in 1980 and is visually almost indistinguishable from the 92F.
In the escape scene early in the movie, De Niro's character Hunter takes a Glock 17 handgun from a guard. This weapon was not manufactured/sold until about 1984. Since the scene is set in 1980 it is somewhat improbable that he would have one.
When Danny and Davies are scouting the Brecon Beacons in 1980, Danny's coat clearly has a Superdry logo on the collar. SuperGroup, the parent company of Superdry wasn't founded until 1985. Superdry as a brand wasn't founded until around 2003.
When Danny first meets his agent in Oman he is standing on the right of the white Mercedes. They talk and after a short while Danny says "Ok Let's go" and immediately steps into the car from the left side.
When Danny, Hunter, and Spike are in the desert at the end of film Spike is standing about 6-8 feet from his car during the sequence. As he watches the others drive away he is now 25-30 feet away and has not moved during the entire sequence.
In the opening sequence in Mexico Danny is wounded in the right shoulder by a gunshot. In the subsequent sequence at home in Australia he is seen wearing a tank top and his right shoulder is completely unmarked.
After Hunter opens the briefcase full of money the position of the paper bands around the bundles of dollar bills and the position of the bundles in his hands change repeatedly between shots during the "hookers and blow" speech.
When the sabotaged truck is leaving the depot just prior to the 'Boston Brakes' job, it is next to a rail yard. One of the locomotives has the insignia of Vic rail/v-line meaning it was shot in Victoria - the south eastern state of the Australian mainland.
The sequence featuring a car chase starting and finishing at the hospital featured many vehicles with license plates showing three numbers and four letters, a format which has never been used in England.
After Danny was playing boxing with Davies some where in Paris, France, they went to an office , on the glass door of the office the word "Manager" was written in Arabic. Which is the word "modeer" but it was written in Arabic letters
When Spike reads Harris' obituary, it says he died in 1980. However, the prologue scene (Mexican assassination) happens in 1980, according to the opening crawl, and Danny learns Hunter has been kidnapped one year later (according to the next intertitle), so Harris' murder must have happened during 1981.
When Spike is about to leave from interrogating Danny, who is lying on the floor and tied to a chair, Danny kicks off a slat from the right side of the chair, trying to free himself. As Spike returns seconds later, the chair is back in perfect condition with the slat unbroken and in place.