During the London race when James is stuck in traffic while explaining why he thinks the Mercedes is so big and unnecessary, in one shot he's in the second lane from the traffic lights behind a black taxi, but when the shot cuts to the front of the Mercedes, the taxi is not there and the Mercedes is in the nearest lane to the traffic lights beside a bus, at the front of the queue of traffic.
In the London race, just before the Stig gets on the bus that takes him to Gunnersbury, you can see a group of schoolgirls walking away from the bus stop. As the bus approaches, the schoolgirls have gone.
In the London race, when Jeremy goes under Wandsworth Bridge, he says "That's the Embankment. Where's May?" when it was actually Hammond who had got onto the Embankment. May was stuck in traffic around Piccadilly and Trafalgar Square at that point.