That will cost roughly £3.5bn to £4.0bn per annum. There was no mention of the cost in the article. Will probably lead to a lot of (over)crowding too, with inevitable demands for more trains / carriages (and less money to pay for them). It's a bit ironic that the bit that is soaking up most money (Network Rail) is the bit that is already nationalised. A further irony: those who commute (or travel by rail generally) tend to be the wealthier. Corbyn will be transferring subsidies to them.
Given that total rail income from tickets last year was £9.8bn 1/3 of that would be a little least than £3.3bn however not all that would be subject to the reduction (such as advance tickets).
If it is only season tickets (circa 45% of ticket income) then the cost would be £1.47bn.
However even that is simplistic, as many have pointed out it would mean that a LOT more people would be wanting to travel by train.
As such you could see that cost fall further as more people use the trains.
Now whilst it is true that there'd be a lot of places where there wouldn't be much spare capacity (chiefly heading into major cities) there's a lot of people who would be willing to use services to other places which otherwise are running with spare seats.
It should also be noted that if someone is paying £6,000 for a London season ticket it falling to £4,000 isn't actually going to attract that many more people to use those services. Why? If you think about it how many actually drive into London for work? Probably fairly few. Yes you may get a few more being willing to look for work in London, but overall is suggest not that many.
Where it's going to make a difference is for those who travel 5 to 20 miles to/from work each day, where there's a lot of the big upfront costs of car ownership aren't spread over that many miles each year.
If that's the case then the overcrowding is likely to be for fairly short distances before someone has a chance to sit down.
Yes there'll be a need to put in more investment to creating extra capacity, however there's probably still a fair amount of extra capacity available for a lot of the country by providing longer trains.
Yes there'll be a need for extra capacity to be created for London and other major cities, but we need that anyway and given that little of that comes from ticket sales anyway it's unlikely to make much of a difference to what is/isn't funded.
Having said that, do I think that is a good idea to have such a cliff edge in ticket prices?
Well that depends on if you think that we need to reduce our car usage so as to significantly reduce our carbon emissions?
Given that I do, such a change is likely to result in a significant reduction in emissions (especially given that most train emissions are assessed on trains being 30-40% full, if we can get that to 35-45% full that reduces the per person emissions by at least 10%, even before you consider the greening of the power grid).
Yes it would create some problems (but I think that'll not be as extreme as some fear) however it would result in a significant cultural shift in how people view rail travel and could therefore result in a noticeable modal shift.
With regards to those who use rail, whilst 42% of rail travel is done by the top 20% by income, is also true that 13% of rail travel is undertaken by the bottom 20% by income. As such although there's clearly a higher usage of rail by those with higher incomes (probably significantly skewed by those working in the City of London) the amount below the average in the lower levels is about 1/3. As such it's not that significant.
It should also be noted that a household with an income of £50,000 could fall into this to 20%, which although it's a decent income level is far from excessive of it's a Cole where both are working.