Good Movie but Why Include Fictional Rubbish?

Rating: 6/10 (19 January 2018)

The movie is largely based on Martin Gilbert's 'Finest Hour'. Many lines of dialogue are taken verbatim. If you want to get a view of Churchill this is the book to read. Churchill's pugnaciousness, burning charisma and appalling political track record come over well.
As a dramatic representation of perhaps 10% of the book it does well overall.
The key roles of the major players: Churchill, Halifax, Chamberlain are accurate.
The bunker, in which much of the movie is set is filmed in the actual place and is open to the public. It drips with history.
The underground railway scene in which Churchill decides to fight on is totally fictitious. It is very unlikely that Churchill ever rode the London 'tube' in his life.
He was born into the aristocracy: his grandfather was the Duke of Marlborough. These people do not listen to people who travel on the tube! They are servants at best and cannon fodder at worst. The notion of people on the tube and Churchill quoting 'Horatio on the Bridge' at each other is laughable.
I am left wondering why the film's producers would go to great lengths to show historical accuracy for most of the film and then let it down with complete rubbish at the end.
This inevitably raises the question 'if this scene is fictitious, what else is?'