Let's just, for a moment, consider a hypothetical example.
If you commute from LAX to LHR, on a 50% contract and have union business also in LHR [for which the union members pay you £100 per day, allegedly] and have been off sick for a year but have recently returned to work, then your commute costs have been about £100 per month. Of course, if you happened to be connected to a union you probably rarely (if ever) travel in the class your ticket entitles you to, and end up being 'comfortable'.
What may the future hold?
Well, a hotline/cheap seat will probably cost £400 return, and current emotions will probably result in any attempt to make the journey more 'comfortable' be a reportable incident, and therefore be in a different class of travel! So, a bit of a change!
Compare this to you commuter from xxx (anywhere from Manchester to Glasgow to Nice to Barcelona) with no Staff Travel.
4 reports a month on Longhaul (more on Shorthaul). Instead of £50 return it's now £80 (but several missed flights due late inbound) so either more fares of many more hours waiting to get home) and either way, probably £200+ per month extra and 20 hours fewer at home - every month.
Do the sums, folks!