Continuity mistake: When the Jeep at the head of the army convoy starts off again, after being stopped at the temporary traffic lights set up by the crooks, the external shots show the Jeep passing the traffic lights. But the next shots from inside the Jeep show them passing the traffic lights a second time.
Continuity mistake: The train that the three crooks are on, when they drop the bag of jewels off, isn't the same train they got on at the station.
Revealing mistake: When the prison van drives through the tunnel, then stops and reverses so the crooks can set up the road works, it's supposed to be driven by Wilfrid Hyde White. But it's obviously being driven by someone else, as the driver looks nothing like him.