For those unfamiliar with fares in London, they are, like many European cities based on a zoning system. The zones run from the centre and each station is in one or two zones.
The zones are important as they are used to calculate your fare on the tube. (Buses have a standard fare per journey).
If you buy a season ticket that includes the central zone, Zone 1, then the price is significantly higher than just having a season ticket for other zones. For example, my Zones 2-4 season ticket is £1,008, whereas if it included Zone 1 it would be £1,744. I don’t travel to Zone 1.
Now, if I have to travel around in Zones 2-4 I am careful not to enter Zone 1. However, it now turns out that just avoiding Zone 1 is not enough, TfL require you to use one their approved routes.
Take my recent journey from Finsbury Park to London City Airport. My chosen route is via Highbury and Islington and Shadwell, but this is a chargeable route. You have to go via Stratford which is much slower and involves a set of stairs where there is no lift as an alternative in order not to have to pay TfL extra.
And how do TfL expect you to know this? Why of course you use their web site and their Single Fare calculator:
The link is here.
Madness if you ask me!