Most people will commute ~19 days a month, given vacations and sickness.
From my example, that's ~794 miles (corrected) a month, £255, £0.32/mile. Not as expensive as some other routes but still can be as as high as 12% of your take-home wage given the low salaries in that city.
Moving onto London... /under/ 20p a mile? Which route is that??
Just some random examples I picked:
Alton to Waterloo: £529, 1786 miles, £0.29/mile.
Guildford to Waterloo: £453/mo - 1140 miles a month, £0.39/mile.
Gravesend to London Bridge: £436/mo, 836 miles a month, £0.52/mile.
Brentwood to Liverpool St: £336/mo, 706 miles a month, £0.47/mile.
St Albans to Thameslink: £440/mo, 756 miles a month, £0.58/mile.
Brighton is £559/mo for the Thameslink only ticket (the cheaper one) and 50.5 miles to London Bridge. Even being generous saying 22 days a month, that's 25p/mile.
Just give up.
I've proved your "A typical season ticket into London is under 20p a mile" claim wrong multiple times.
Southampton to Waterloo is just about the exception at ~19p/mile if you assume 22 days per month which I think is exceptional.
Annual tickets are 40 weeks meaning 5.75 trips per weekly ticket (230 a year). Newbury works out 21p a mile, Ipswich 23p a mile, Cambridge 22p/mile, so yes prices have crept up just above 20p/mile in the last year or two.
From my example, that's ~794 miles (corrected) a month, £255, £0.32/mile. Not as expensive as some other routes but still can be as as high as 12% of your take-home wage given the low salaries in that city.
Moving onto London... /under/ 20p a mile? Which route is that??
Just some random examples I picked:
Alton to Waterloo: £529, 1786 miles, £0.29/mile.
Guildford to Waterloo: £453/mo - 1140 miles a month, £0.39/mile.
Gravesend to London Bridge: £436/mo, 836 miles a month, £0.52/mile.
Brentwood to Liverpool St: £336/mo, 706 miles a month, £0.47/mile.
St Albans to Thameslink: £440/mo, 756 miles a month, £0.58/mile.
(Mileages from https://www.scotrail.co.uk/carbon-calculator )