Phil Richards wrote:

In all fairness rail and tube fares ought to be the same. Certainly most
other cities abroad where a zonal fares applies, a ride on the metro
costs the same as surface rail for the equivalent zonal journey.

Agreed. This might result in an increase in rail fares, but also a
decrease in Tube fares, which are getting a bit silly.

What we *ideally* want is a true Verbundtarif (joint tariff), where you
buy a public transport single, return or Travelcard and may use as many
or as few modes to complete your journey as necessary. To do anything
else is to penalise those who don't have a choice but to do so.
However, the offensively high tube fares[1] and relatively low
(especially on Oyster) bus fares are incompatible in this respect, so
perhaps a free bus ride with every Tube ticket but not vice-versa would
work.

[1] I realise that this is, at least in part, a capacity management
issue that doesn't exist in most other countries.

Neil