I've never had anyone check I've actually got a First class ticket in the Newcastle lounge.
I quite believe it.
last November for my wife's 60th we had a trip to London, our first train journey for probably 20+ years and we loved it. We've had a few trips since then (Edinburgh, Glasgow, London again and a couple of weeks ago Manchester & Liverpool and despite having a two Together railcard, i think we have shown it once.
We travelled to Manchester via Doncaster (on LNER) then on TPE first class. Nobody even checked our tickets, let alone railcards.
For long, city-to-city trips it's probably a case that very few folk are cheating, but you would still think tickets / railcards would be checked every time. I would imagine the extra cost of an invalid ticket plus maybe a fine would be worth the effort.
On the Tyne & Wear Metro, you see inspectors once in a blue moon and the stations are not manned .. so the ease of travel without a ticket is high. It would seem to me sensible to have more regular checks.