Richard M Willis wrote:

Why does routine payment of a PF constitute evidence for prosecution ?
There's no law against deliberately paying a PF and doing so every journey.

There is; the railway byelaws require the purchase of a ticket before
starting the journey unless no opportunity is available to do so. This
makes an utter nonsense of the whole concept of PFs.

Far more sensible would be to decriminalise ticketless travel, and
instead enforce only by way of increased PFs on a similar model to
parking tickets.

Neil