Rail infrastructure operator Network Rail has opened a consultation into building new rail lines - which could be high speed lines - along five of its most congested corridors.
The strategic review will look at five strategic routes, north and west of London: Chiltern, East Coast, West Coast, Great Western and Midland Main Lines.
The Conservatives have said they will back high speed rail in any coming election.
Network Rail chief executive Iain Coucher said: "By 2025 many lines will be full up, especially those running to and from the north and west of London. This will happen even after we have implemented the investment to boost current capacity.
"With popularity for rail growing, we have to start planning for the medium- and long-term future today. We have to see how we can meet the capacity challenge and see what solutions – including potentially, that of new lines – are deliverable and affordable. This review, working in partnership with other players in the railway industry, will kick start this process.
"Network Rail is uniquely positioned to take a network-whole approach in planning the railway of the future. We have a thriving railway today and that must continue and grow to meet the economic and environmental needs of tomorrow's Great Britain."
Congestion on the rail network is predicted to increase in the coming years, with a 40% increase in passenger numbers in the past 10 years alone, now carrying 1.13bn journeys per year.
Today some 22,000 services run on weekdays – up from 17,000 at the time of privatisation. Freight has also increased by 60%, although from a lower starting point.
Network Rail has launched a tendering process to appoint a consultancy to assist this study.