The number of rail journeys taken in a year has more than doubled since the mid-1990s, according to official figures.
And it is journeys to and from London and also within the capital that has driven the most-recent annual increase, the statistics from the Office of Rail Regulation (ORR) showed.
Overall, there were 1.27 billion rail journeys made across England, Scotland and Wales in the 12 months ending March 2013 - a 3.3% rise on the figure for the 12 months ending March 2012.
There was a 2.8% increase in journeys to and from London in 2012/13, while journeys wholly within London rose 6.3 million.
The increase between 2011/12 and 2012/13 for Scotland was 2.9% both for journeys to and from Scotland and for journeys within the country.
Journeys wholly within Wales in 2012/13 rose 1%, with the largest rise (of 7.8%) being on services to and from the South Wales town of Merthyr Tydfil where demand has grown by more than 60% in the last five years.
Campaign for Better Transport's Martin Abrams said: "These figures are remarkable and show just how integral trains our to the economy and to people's lives.
"The success of the railways is not without problems. The London economy relies on trains, but there is increasing anger among commuters at the high cost of getting to work. There is also a big disparity in the quality of services in London and the south east compared with parts of northern England."
He went on: "The comparison between Scotland and Wales is stark, with devolved management of services in Scotland delivering significantly better results for journeys being taken by train than the equivalent in Wales."
"We need our railways to support all parts of the country. That means stopping fares rising faster than wages, investing in those areas which are under performing and giving local bodies more control over decision-making to make sure spending goes to the right places."
Mick Cash, acting general secretary of the RMT transport union said: "While passenger numbers on Britain's railways continue to surge, the capacity required to meet that demand has failed to keep up, leaving many services bursting at the seams with in some cases passengers left stranded because there simply isn't enough room on board."
He went on: "Rather than the cuts to staffing set out in Sir Roy McNulty's (2011) rail review for the Government, what we really need are more engineers to deal with maintenance and renewals, a speeding up of the fleet replacement programme to expand capacity and more staff on trains and stations to ensure safe and efficient operation.
"Britain's railways are a stunning success story but we could be doing a whole lot better with proper investment in capacity and modernisation, free from the profiteering and exploitation of the private train operators."
A spokesman for rail industry body the Rail Delivery Group said: "An industry focused on attracting more passengers and freight, combined with a commitment by successive governments to invest over the long term, is generating phenomenal growth.
"This winning formula is helping to reduce unit costs while improving and expanding a vital public service."