It's cheaper to purchase new bike/used car, tax and insure it, service and fuel, than to use train to ride to work.
Annual train ticket form my small town (25 miles from the Zone 1 of London) is over £5,500. Five GRAND. For the pleasure of standing every time and a much higher risk of getting mugged.
£15k will give you REALLY nice bike or pretty new car. After third year you're saving thousands. Of course if you decided to buy something old and used, you're saving from the second quarter of the first year on.
It's only functional because not everyone can afford another car to work.
It can be, depends on a lot of factors. Obviously flying ryanair will often be the cheapest way to go, but if you do any sort of other regular airline trains will quickly start to win out.
And it's not as if you can fly everywhere in england. As soon as you start looking at more oddball flights (for example, london to birmingham) ryanair goes away as an option and all the flights end up super expensive.
Trains, on the other hand, remain cheap for pretty much the entire nation. You can basically go anywhere by train for under £60. A lot cheaper if you book in advance.
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).