Factual error: As the Royal Navy has its own police (including detectives), there would be no need for a civilian detective to be airlifted onto a submarine, especially to investigate a sudden death that was not originally believed to be a murder.
Suggested correction: The Royal Navy police are not equipped to handle murder; local police are usually used for more serious offences so no claim of a cover up. There are no MoD police attached to a submarine either, so in theory somebody would have to go to the boat. (However they still wouldn't risk surfacing).
Initially there is no suspicion of murder, only an unexplained sudden death. There would be absolutely no need to airlift a civilian detective aboard a top-secret submarine. It wouldn't be the first time a sudden death had occurred aboard a Royal Navy vessel.
Family Day - S2-E5
Factual error: The phone number Harry is given has an exchange that starts with "0" (the first 3 digits after the area code). Phone numbers (in the US) can't start with "0" since that's the "operator."
Factual error: The fly Good Chucky kills bleeds red blood. Fly blood is usually clearish with a yellow and green tint. Not opaque red.