Assume every tax rate except for the "personal allowance" was increased by 1% to fund free train travel. That would mean someone at the median annual income of £38k would pay about £254 extra tax per year ((38000 - 12570) * 0.01)

Would you be in favour of this?

Some numbers for context:

The government raised £17.1 billion in 2024.

The ScotRail revenue for 2024 was £351m (page 17).

So to offset the cost of tickets, the government would have to raise £351m which divided by the 2.46 million people in work would be an average cost of £140 extra per person collected per year, so I believe 1% may be able to pay for it comfortably, and even improve the service, to compensate for the extra demand on free travel.