After the mob throws a Molotov cocktail through the Carlo's Ristorante window, a fireball bursts back out towards them. The only way to create such an explosion would be if the room was full of natural gas. Molotov cocktails are designed to start a fire by spreading a burning accelerant over a maximum area rather than forcefully exploding.
It is stated that Lawrence Gasgoine was paid a £2,000 bribe by Raymond Brooks, that would have been a huge amount of money in 1940, equivalent to over £100,000 in today's money, £100 would be more believable.
The Hand Grenade that was tied with a wire to the doorknob as a booby-trap is an American Mk2 "Pineapple". While the grooved cast iron "pineapple" shape design is similar, the top part is different to the standard Mills Bomb Hand Grenade standard use by the British. The British never use American grenades in their service as it has its own Mills Bomb.
It can even argued that the American Mk2 grenade was even in the wrong time to make an appearance in Britain as the episode takes place in 1940 while the Lend Lease was in effect only in Spring 1941. American arms and munitions cannot be in Britain during that timeline.
It can even argued that the American Mk2 grenade was even in the wrong time to make an appearance in Britain as the episode takes place in 1940 while the Lend Lease was in effect only in Spring 1941. American arms and munitions cannot be in Britain during that timeline.
At the beginning of the episode you can see a man cutting the railing with what sounds and based on the sparks, looks like an angle grinder. The angle grinder was not invented until 1954 which would have been over 10 years after the episode was set.
At the dance, the saxophone player is obviously not actually playing the instrument, as there is no finger movement on the valves.
At the end, Foyle is sitting in his office and the conical fire extinguisher on the wall is upside down. These were water fire extinguishers and were stored point up, otherwise the water would have run out through the hole in the top.
Sam and Tony Lucciano go to a dance. We see a saxophonist playing a tune but his fingers do not move on the keys. Later we see his fingers moving.
Joe and his father, Eric, share the name Pierson, yet they are credited as Cooper.