In message , at 10:06:21 on Sat, 3 Nov
2012, Peter Smyth remarked:

No allowance for standing is made on a service when the time between
stations before (AM) or after (PM) the critical load point is more than
20 minutes

Which is what applies to the train I was describing.

In some cases train operators do not have standing capacities
calculated for their rolling stock based on the available floor area.
In these cases the standing capacities have been estimated as 20 per
cent of the number of standard class seats for long distance rolling
stock, and 35 per cent of the number of standard class seats for
commuter rolling stock. These estimates have been used for Arriva
Trains Wales, CrossCountry, East Midland Trains, East Coast, First
Great Western and Virgin Trains.

Although there can't be many trains run by those operators on the main
lines that come in under the 20-minute rule.
--
Roland Perry