Our booking engine at tickets.railforums.co.uk (powered by TrainSplit) helps support the running of the forum with every ticket purchase! Find out more and ask any questions/give us feedback in this thread!
Network Rail has also borrowed against specific assets for certain upgrade projects too, take the Chiltern upgrade, for which the franchise pays a facility charge in respect of.
Its also the main way of financing improvements as the Government doesnt really cough up enough hard cash. You want to spend £200m improving a major station or a billion on line improvements? NR borrows the money and repays it over a 30 year period by putting up track access charges.