I have long suspected this ‘only 2 left’ business is not really true in any case. Weirdly I have no such concerns when looking at nationalised booking engines in Europe. Funny how there is a real trust deficit building up now between passenger and UK rail company.
Companies aren't allowed to just make up the urgency prompts, and they can be fined quite a lot for doing it, but as with everything else there is essentially no enforcement, so a huge proportion of them are either a complete work of fiction, or actually presage the last opportunity to a higher amount before the lower desperation fees kick in.
Trains and planes do largely seem to be an exception to this though. You get the occasional price drop if the advance pricing turns out to have been wildly wide of the mark, but for the most part there's a quota and when it sells out the advance fair moves up to the next tier.
The only thing that makes it a bit wonky is that train ticket retailers offer a huge 2 hour window for you to complete the transaction, so you'll sometimes get somebody go to buy 6 tickets, exhausting the quota, and then change their minds, so the price or "last 2" offer goes back down. I've quite often managed to temporarily lock myself out of a price band for tickets this way when the browser has died partway through or the site has gone down.