When Donna returns home there are no cars visible as she spots Wilfred but when she runs towards him she passes a car on the left side of the street.
The UNIT command post is in a tractor trailer, but it is quite a lot larger inside than out, despite not being a TARDIS.
Guns are prevented from firing by a field that expands the bullets' copper jackets. This would not stop the firing pin from detonating the gunpowder. Yet several people pull the trigger on their weapons with no explosion.