Just read an @tfl prosecution notice sent to a friend of mine (thought she had tapped in her debit card successfully on a bus; she hadn’t). Lamentably obscure.
Offence mis-stated (by comparison to the relevant regulations) perhaps significantly. No attempt to explain the level of possible fine (just a generic reference to the sentencing council). Pages loose and not numbered, so hard to keep in order.
Finally, the public version of the relevant regulations on legislation.gov.uk is out of date and doesn’t contain the offence she is charged with. I had to look it up on (paid-for) Westlaw. This is not OK: it’s contrary to the rule of law. @MoJGovUK @neill_bob
And in the circumstances @tfl should have an up to date version of the regulations on its website, and provide a link to them in its material.
Cc @SadiqKhan
(PS criminal lawyers will be relieved that my advice was to go and see a criminal solicitor - she is for various reasons worried about getting a criminal record, so this matters to her. First rule of being a good lawyer: know your limits.)
PPS The @TfL prosecution policy is useless. The head para under 6.3 tells you nothing. And for a fare mistake like not tapping in correctly, 8.1(f) will always apply. And how is an ordinary person supposed to know about (e)? 
As to pointers against prosecution, none of these factors apart from the medical one would ever apply to a case such as this (see the footnote to (b)).
So it is really impossible to tell when @TfL will decide to prosecute a genuine mistake as to whether you have tapped in correctly. Something that could happen to any of us, any day.
You are, it seems, left entirely dependent on the whim of an official as to whether they’ll accept a penalty fare or prosecute (with a fine plus £225 prosecution costs on a guilty plea, the notice says).
NB my friend was able to show she took the same bus every working day and paid for it. Made no difference to @TfL: not prepared to impose a penalty fare for a genuine mistake; prosecute anyway, taking up court time, imposing a criminal record, and demanding prosecution costs.
