That wouldn't be the Union Jack then, but a blue ensign (or whatever variation of the blue ensign Trinity House use). It is an odd quibble as another commenter

That wouldn't be the Union Jack then, but a blue ensign (or whatever variation of the blue ensign Trinity House use). It is an odd quibble as another commenter put it - I guess being well-researched is exactly what makes pieces like this interesting, so I was struck by how easily an errant detail distracted me from that - especially one that could so easily have been omitted.