I'm sorry, but I don't quite follow your logic.
Surely since in this example the passenger is 'travelling London - Leicester' it's entirely reasonable for them to be issued a ticket (in the form of a penalty fare) that will allow them to complete their journey rather than on something that they might do. Does the railway officer know if the passenger's priority is to save money (by stepping back to the next Kettering to Leicester service) or to get to Leicester on time?
What's "reasonable" is irrelevant - the PF must be issued in accordance with the PFR. The PFR themself might make reference to "reasonableness", but there is no inherent test of reasonableness that entitles them to simply ignore the actual law - PFR.
Indeed, what the government said isn't going to override the meaning of the legislation, but in this case, as the government has said 'we increased the value of the penalty fare to £100, plus the price of the single fare to the intended destination' (my bold) then to my (non-lawyerly) eyes this suggests that the intention of the legislation was that the penalty fare would be to the point where the passenger expected to get off the train (Leicester rather than Kettering in your above example)
Or we could look at what the government said was the point in your earlier quote - see above.
We can't simply ignore what the legislation actually says in favour of what the government says.
You can read here if you wish -
https://supremecourt.uk/uploads/speech_lord_sales_240919_1e4f3f8d1f.pdf
We often say that we are looking for the intention of Parliament, but that is not quite accurate. We are seeking the meaning of the words which Parliament used. We are seeking not what Parliament meant but the true meaning of what they said.
So we definitely cannot simply ignore the actual words of the legislation and say "well they intended to go to Leicester, because they'd previously purchased a £20 Advance, so they definitely still want to go there now it costs £138".
And again, "It has always been said to be important to consider the "mischief" B which the Act was apparently intended to remedy."
As I observe, the "mischief" here appears to have been "too cheap" PFs, inconsistent, unfair or confusing rules (the old penalty was effectively the greater of (£20-fare) or (fare), whereas now it is simply £50), and inflexibility (you need to get off at the next stop)
In stating "that the passenger may specify" it does appear that the passenger is the one given the flexibility.
It doesn't appear at all that Parliament intended for the passenger's choice to get off at the next stop (or in practice buy a new ticket online) to be taken away from him especially given that this reintroduces much of the inconsistency/inflexibility that the PFR amendments seem intended to have done away with.
Nor is it all logical that the passenger should be expected to say "actually I'm going to get off at the next stop instead" when faced with an RPI trying to charge him £££££ in a PF. The passenger has no idea what is going on, whether he is entitled to ask for this - it can only make sense that the RPI must ask.
Do we consider paying the walkup fare to be a penalty? In that case, there's an awful lot of commuters being punished every day that they use the train.
Clearly passengers who choose to buy a ticket for £138 in advance are not being penalised, because they chose "London - Leicester", saw the price, then clicked "Purchase".
However, passengers who are simply charged £188 to their final stop because they are told they made a mistake, where there in fact exists the option to pay, say, £100, to the next stop, are not in the same position of free choice and negotiating power.
But on my analysis, that's not a full statement of what what the legislation says - it allows for the scenario where the customer is clearly going to Leicester and shouldn't be compelled to enjoy the delights of Kettering.
It would be nice if we could show that the legislation was more supportive of passengers than the railway think it is. But in practical terms of giving advice, we need to be clear as to what the law is, and give our advice based on that - not on what we think the law should be.
The full statement of what the law says is
"
(2) Where a collector charges a penalty fare, the collector must provide that person with the following information in writing at the time the penalty fare is charged—
(a) a statement that the person is being charged a penalty fare;
(b) an explanation of why the person is being charged a penalty fare;
(e) the penalty fare number;
(f) the amount of the penalty fare;
(2A)
the information provided by the collector must also include—
(b) where the penalty fare authorises a person to travel, the station to which the penalty fare authorises the person to travel.
(5A) the penalty fare charged to a person travelling by or present on a train authorises a person to travel to
(a) a station in England at which the train is due to make a scheduled call that they may specify, if the collector considers that this is reasonable in all the circumstances; or
(b) otherwise, the next station at which the train is due to make a scheduled call.
There is no
other law than this one, and anything stated elsewhere is
not law. It
might help us to understand what is meant by "specify" to look elsewhere, but we can't just ignore the word "specify", and say that the law says "intended station", because that is not correct, and isn't the law. It's the station the passenger "may specify".
Sometimes the passenger has a ticket, sometimes not.
We might decide that in the context of the above that simply by showing their ticket to Leicester that they have "specified" that.
However that doesn't seem to me to be true. If I board a train at Coventry and shortly after present an invalid Coventry - Chester ticket, then it wouldn't be lawful to issue the PF to Chester, since it's not a stop on my train, and I could potentially be travelling on the current train to one of several different stops, and it clearly would not be correct for the RPI to just issue it to Wolverhampton without asking me.
Similarly, I usually buy my ticket to a later stop, because it's the same price. My intended destination is B, but my ticket says C.
In addition, a passenger may well be intending to break their journey, so unless the ticket is "no break of journey" the fact that a ticket says "Edinburgh" on it, doesn't mean I had or have any intention of travelling there on the current train.
It isn't hard for the RPI to ask the passenger. It is not the passenger's fault if the RPI fails to do so.