The Passenger Railway Services (Public Ownership) Act 2024, which passed last week, allows the government to take rail contracts back into public ownership.
The government plans to set up a new arms length body, Great British Railways (GBR), which will take over service contracts currently held by private firms as they expire in the coming years.
It also eventually wants GBR to take over responsibility for maintaining and improving rail infrastructure from Network Rail.
Responsibility for running train services was handed to private companies during the 1990s, and since then there has been a boom in rail usage.
But a number have faced criticism over fares and reliability, with critics saying privatisation has led to an inefficient and fragmented system.
Labour made it a manifesto pledge to renationalise most rail services within five years.
During the coronavirus pandemic, the government in effect took control of the railways.
Most train companies in England moved onto contracts where they get a fixed fee to run services, and the taxpayer carries the financial risk.
Four major operators – East Coast Mainline, TransPennine, Northern and South Eastern – have been taken under public control and are being run by the government’s operator of last resort.
Transport for Wales was brought under Welsh Government control in 2021, and Scotrail was taken over by the Scottish Government the following year.
South Western Railway has more than 1,500 services scheduled to run per weekday in south west London and the south of England.
It operates across a huge area of southern England and is a key commuter service into London.