Andrea wrote:

However, I have found that these operators now have an off-peak 'First
Cheap Day Return'. FCC have this, as does FGW. Why do very few
people take up these offers, which seem to be good value for money?
Is there a general assumption that First Class is far too expensive?

It often is, for what you actually get. The quality varies dramatically
between operators, though. For example, on Southern Electrostars the First
Class consists of nothing more than an antimacasseur on your seat back. The
seats are EXACTLY the same as in standard class, at the same pitch and
spacing and many of the ones in Standard are arranged 2+2, the same as in
First Class. Off-peak you might be lucky enough not to get someone sitting
next to you but, from the number of people that I see on Southern, that
blatantly ignore the FC markings, it isn't worth even considering.