The study, carried out for Transport 2000 by researcher Roger Ford, finds that the cost of many types of work is more than twice that at privatisation ten years ago.
According to the study, the cost of the West Coast Main Line modernisation stands at around £10.2 million per kilometre. By contrast, the East Coast Main Line modernisation in the 1980s cost £1.1 million per kilometre at 2000-01 prices.
Transport 2000 public transport campaigner Mick Duncan said: "Privatisers' hopes have not been matched by reality. Costs, subsidies and fares have rocketed and performance deteriorated."
The total subsidy in British Rail's final year as operator of an integrated railway was £1,325 million at 2003-04 prices, the study says. It is expected to total £3,840 million for 2003-04.
The report adds that fears over line closures, service reductions and declining passenger numbers have not been borne out.
"Network Rail's takeover of maintenance work and the Strategic Rail Authority's hands-on approach to franchising represent a more integrated and interventionist railway than the government tried to create," it says.
The Rising Cost of Britain's Railways is available from Transport 2000 (tel) 020 7613 0743.