And a report to the House of Commons report on the THE IMPACT OF 1ST CLASS ON CROWDING ON UK TRAINS
One way to reduce the impact would be to abolish 1st class altogether. Another is also suggested in the report:-
"12. Carriage Conversion
One way to deal with the issue of crowding would be for train operating companies to convert at least one of their first class carriages to standard class on every full train set. In the case of Virgin’s Pendolino sets, for example, this would increase total standard class seats by at least 62 seats and reduce first class seating capacity by at most 46 seats. If current average utilisation rates in first and standard class are assumed to be 35% and 65% respectively, first class occupancy would increase to 51% whilst standard class would drop to 54%—assuming no passenger switches class. In other words, first class, which is inherently more comfortable than standard class, would remain less crowded than standard class. If two carriages were converted, the occupancy levels would become c85% and c45% respectively. This suggests that at peak times first class would reach capacity—although this could be readily “managed” by reducing the number of “discounted” first class tickets sold."
They could also, of course, just temporarily relabel the 1st class carriages as standard during rush hours, thus freeing up ALL the seats in them to the standard class passengers.