"Functional train system" is not how anyone would describe the UK. It's cheaper to fly than take the train.
Cost to fill up doesnt matter, only the cost per mile.
That is because of the cost structure of trains vs planes. Trains require a huge amount of infrastructure, and have higher labour costs because they are slower (so the same journey means people work for longer).
£3.20/320 miles = 1p/mile
~1.5 billion train journeys a year is “functional”.