The gold bars which are stolen in the robbery would weigh around 10 to 15 kilos each; there is no way that 'Brain' could lift them in one hand so casually to load in to his camera case. Similarly there are at least 4 in the case when Serge picks it up to load into the car with very little apparent effort.
For many weeks, the team are shown parking up in a white Renault van, and travelling on foot for 1.7 Km through the sewer system, before returning at daybreak, carrying the spoil, clambering back into the van and driving away. On the night of the heist, the crew turn up in a Landrover, carrying the necessary tools, remove the gate, and drive into the sewer system. The Landrover then returns before daybreak to collect the team and their ill-gotten gains. Why didn't they use the Landrover from day one, to remove the spoil and save them the walk each way?..
When the team finally break through from the sewer into the bank's vault, the gas cylinders they use have 'Calor' stamped on them-unlikely, as this company supplies the UK and Eire only. The French equivalent would be 'Elf' or 'Camping Gaz'.
Although the British cast are fairly good at sticking to metric measurements, when asked how large the tunnel from the sewer needs to be, Fernand answers 'four feet', something a Frenchman would never say-more like un mètre et demi-'one and a half metres'...