UK trains are the oldest since current records began, a probe has revealed.
Carriages on Britain's track were typically built in the mid-1990s, according to the Office of Rail and Road.
An analysis by the Press Association found that the average age of 21.1 years is older than at any point in publicly available records and 60% older than in 2006.
Older trains often result in worse reliability, less comfortable journeys and poorer performance, the ORR has previously warned.
Travellers using the Caledonian Sleeper service between London and Scotland have to put up with Britain's oldest trains at 42 years old.
Merseyrail, which runs trains in Merseyside, has the second oldest fleet at 38 years old.
Both operators plan to introduce new rolling stock in the coming years.
TransPennine Express, which operates in northern England and Scotland, has the newest trains at an average of just nine years old.
"We've been promised new trains by several train operators and some are under construction - we now want to see these promises turn into reality," said Stephen Joseph, chief executive of the Campaign for Better Transport.
"While some, like the famed Pacers in the North of England, do deserve the scrapyard, others can be refurbished to modern standards and could help deal with overcrowding on parts of the rail network."
ORR data shows the average age of rolling stock between January and March each year since 2001.
A number of new trains were introduced following the end of British Rail in the mid-1990s but the average age has risen during the past decade.
The Rail Delivery Group, representing train operators, says more than 5,500 new carriages will be in use across Britain by the end of 2020 and many other trains are undergoing multi-million pound refurbishments.
"This will help to deliver our commitment to boost customer satisfaction so that Britain continues to have the most highly rated major railway in Europe," said Chief executive Paul Plummer.
Trains in London and south-east England are typically 18 years old, while regional services are 24 years old.
A Department for Transport spokesman said: "We are investing record amounts in delivering the biggest rail improvement plan since Victorian times to improve services for passengers - providing faster, better and more comfortable trains with extra seats.
"Passengers all over the UK will be travelling on brand new trains within the next 18 months.
"We have introduced new trains on routes across the country, upgrading trains on other routes, and removing the outdated Pacer trains from the North."