David of Broadway wrote:

Having just come from London, with its fare integration, on a National
Rail ticket that I was told would be accepted on either First Capital
Connect from King's Cross or on 'one' from Liverpool Street, this caught
me by surprise. But apparently it's London and National Rail that are
the exception, not the rule.

What happened with National Rail was a bit of learning from the
mistakes of bus deregulation, albeit by introducing other mistakes. I
hate to think how things would have been if the bus free-for-all had
hit the rails.

There are, in certain areas, interavailable tickets. They aren't the
rule, though, and they are inconsistent and complex. Visitors not
wishing to have to argue the point about whether a given ticket is
valid or not are probably best off just buying cash singles from the
driver, noting (!) that bus drivers are usually only happy to accept
the note "above" the fare (i.e. £5 note for a fare less than £5, £10
for a fare £5-£10 etc) as they tend to carry limited amounts of
change, and that in a very small number of places (e.g. Birmingham)
there are exact change policies.

Whatever "Uncle Ken" does with his overcharging for singles, London is
still far better off...

Neil