Transport Secretary Alistair Darling could announce a review of the railways on Monday to examine devolving some power at the Strategic Rail Authority (SRA), which oversees public rail spending, newspapers reported on Sunday.
Sources told Reuters that the government was planning a review but had not yet set a date.
"There is nothing we've seen in the speculation that would appear to suggest bondholders' and shareholders' interests in the train operating companies or future debt raisings by the infrastructure owner are under threat," a source told Reuters.
A second source said: "The notion that the railways remain a public-private partnership is not at risk. If we took nothing as being zero on the scale of change and re-nationalisation being 10, I don't think we're anywhere near 10."
The Transport Department said the reports, which included proposals to bring health and safety issues on the railways under direct government control, were "pure speculation".
The collapse of the privatised track owner Railtrack in 2001 after the government withdrew funding has made many financial institutions wary about investing in rail infrastructure.
Some 45,000 Railtrack shareholders are suing the government.
The state-backed and debt-funded Network Rail took control of the country's 33,600 km (21,000 miles) of track, 2,500 stations and 40,000 bridges and tunnels two years ago.
The government blamed the ballooning costs on Railtrack after a fatal crash at Hatfield, north of London, in October 2000 exposed the parlous state of the investment-starved network and forced thousands of speed restrictions and train delays.
The centrepiece of government plans to modernise the railways after decades of under-investment in the run up to privatisation in the mid-1990s is its 10-year rail plan to attract 34 billion pounds ($62 billion) in private investment.
John Armitt, chief executive of Network Rail, which has brought in-house all rail maintenance to reduce costs, has said it would take up to five years to build a sustainable railway.
Sources also said the review might examine the independent Office of the Rail Regulator, which sets track access charges, and its relation to public spending policies and commitments.
The rail regulator unveiled last month a 22.2 billion pound five-year budget for the country's railways, less than Network Rail asked for, and called on the operator to clean up its act.