Clive Feather:
Check the timetables. If they show first class is available on a
service, you need a first class ticket to sit in first class. If they
show it as standard class only, you can sit anywhere on the train with a
standard class ticket, irrespective of what the seating is like.

So why is this allowed? I have no problem if the train operators want
to use their first-class rolling stock this way, but it seems obvious
to me that they should be required to mark it as second class, instead
of requiring passengers who don't buy first-class tickets to know which
trains the timetable says first class exists on.
--
Mark Brader | "And so it went. Tens of thousands of messages,
Toronto | hundreds of points of view. It was not called the
| Net of a Million Lies for nothing." --Vernor Vinge