A shot of the exterior of Edgware Road station shows a sign pointing to the 'Hammersmith and City' Line. This wasn't named as such until 1998 and would therefore have still been called the Metropolitan Line in 1970.
Although the film is set in 1971, signs on various shop doors seen in the film advertise that credit cards "Visa" and "Mastercard" are accepted. The name "Visa" was not used for the charge card before 1977 (replacing Barclaycard in the UK); "Mastercard" was "Master Charge" until 1979.
A Revox B77 reel to reel tape recorder is used by the ham radio operator to record the walkie-talkie traffic of the bank robbers. While the movie is set in 1971, the B77 recorder was not released until 1978.
A shot of the exterior of Baker St. station includes a glimpse of the upper section and roof of a London bus driving by at speed. However, it is possible to deduce from the 'straight' rectangular shape of the bus' roof that it is one of the new generation of front-entry buses, possibly the DMS series, first introduced in London in the mid-70s. Prior to this time, the most common double decker buses in London were the Routemaster (RM), introduced in the early 1960s, and the ubiquitous RT, the definitive London Bus, first introduced in the mid 1940s, both of these bus types having narrower roofs with rounded edges. So there is no way that the bus in this particular shot could have existed in 1971.
The Underground train used in the film would not yet have existed in 1971 since it is a 1972 Tube Stock train (based on the earlier 1967 Victoria Line trains) and did not enter service on the Northern Line until 26th June 1972. In 1971, the Northern Line (Tottenham Court Road) would have had the red-painted 1938 Tube Stock, and the Bakerloo Line (Edgware Road to Paddington) would have had both the red-painted 1938 and 1949 Tube Stock.
Paddington station is shown as restored with new British Rail signs. In 1971, the station would have been rather dirty from the steam days and many of the main signs would have still been original. Also, the train carriage is of 1973 vintage.
Near the end of the film when Terry and Martine are together on the Tube train, the train driver or guard makes a 'next stop' announcement over the PA system, but neither had the facility to make such announcements in 1971.
Martine (Saffron Burrows) reads from a newspaper and comments: "police last night were trying to hone in on a £300,000 bank raid, they still don't know what bank it was". The amount of money stolen could not be known or even estimated until the bank from which it had been stolen was known.
The use of the thermal lance is unrealistic. A skilled operator would check the gases are on and at the correct pressure before ignition, rather than relying on a third party to "turn on the oxygen" at the cylinder. As both the oxy-acetylene torch and the lance have shutoff valves, the operator could isolate all the gases if required. Since Bambas was the expert on drilling / tunneling, it is unlikely he would have allowed anyone else to operate the lance, as they would have had no experience of it.
The bank robbing team use a jackhammer to first break through concrete, then continue to use it to tunnel through the soil towards the bank. Jackhammers are of no use in soil. The bit simply plunges in, and accomplishes nothing.
Terry and Martine are on the tube train heading to Paddington, and inside the train, the line map above their heads shows that they are on the Circle Line. If they really were on the Circle Line, they would be on either a then-new C69 Stock train, or an older CO/CP Stock train, not a Tube Stock train. Also, Edgware Road (Where Kev got off) would have been an open air station, not a deep level tube station.
When they reach an open space under the bank, we see a stone which bears the inscription "AGNVS DEI MISERERE NOBIS MDCLXV" and Guy Singer (played by James Faulkner) erroneously quotes it as saying "LAMB OF GOD, FORGIVE OUR SINS." It actually translates "LAMB OF GOD, HAVE MERCY ON US 1665." 1665 is a reference to the time of the Great Plague of London, the last major epidemic of bubonic plague in England, which lasted from 1665 to 1666.
The uniformed officer at Marylebone Police Station (responsible for the area in question)had a letter 'P' on his shoulder. Marylebone Police Station (DM) was(is) in 'D' Division of the Metropolitan Police, so it should have been a 'P'
The movie's opening sequence ("Caribbean 1970") plays the T. Rex song "Bang A Gong (Get It On)," first released in September 1971. But it is only in the soundtrack, and the characters in the scene do not hear it.
Since they did not know about the catacombs before starting their tunnel, there would have been no way for them to be able to use the thermal lance as depicted in the film. The length of the steel rod used on the lance was quite long (8 feet or more) which meant that they would have had to dig another hole straight down beneath the vault just to be able to use it properly. There wasn't enough time in the plan for the extra excavation.
When Terry begins to peel the tiles from the floor of the boutique, the glue used to hold them has a "fresh and liquid" appearance. Tiling-adhesive dries to a very hard and dry state making a "clean removal" next to impossible.
The goof items below may give away important plot points.
Towards the end of the film where one of the robbers is suffocated to death with a plastic bag, in the light blue Mercedes, the car's registration plate ends in 'L'. The 'L' series is 1972/1973 plate, the newest registration plates at the time the film was set would have been 'K' and even in September 1971, that would have just come out.