Witnessed exactly this on a weekday morning train a couple of weeks back. A surprising (to me) number of people wanted to upgrade and were dealt with without fuss. Nobody said no.That's not EMR policy, upgrades are always available from the train manager via the host provided there's space.
Standard method of operation for hosts to be professional is to ask any standard ticket holders in first class "are you wanting to upgrade?" as an opening gambit rather than make the abrupt "this is first class!" type comment.