Rail carriages across Britain will see an upgrade next year after the industry body representing train firms promised passengers an improved service following fare increases.

The Rail Delivery Group, which brings together train operators and Network Rail, said it will be the biggest introduction of new rolling stock in decades.

Hundreds of new and refurbished-like-new carriages will be rolled out up until 2021 – with more seats, improved accessibility and air conditioning.

The rail industry announced last month that rail fares will increase by an average of 3.1% on January 2, the largest rise since January 2013, according to Office of Rail and Road data.

Paul Plummer, chief executive of the Rail Delivery Group, said in November the money from fares underpins improvements to the railway, and will mean “more seats, extra services and better connections” for passengers.

The operators introducing new carriages include South Western Railway, Trans Pennine Express and Northern. Govia Thameslink Railway passengers will see 150 new carriages replacing trains from the 1970s.

David Sidebottom, director at independent watchdog Transport Focus, said: “For passengers who have put up with much inconvenience in the expectation of a better, more reliable rail service, the prospect of more seats and new trains will clearly be welcome.

“Passengers tell us their top priorities for improvement are more trains arriving on time, more chance of getting a seat or standing in comfort and better value for money services.”

Mike Cherry, national chairman at the Federation of Small Businesses, said: “In the 21st century, you should be able to run your business from a train.

“As well as ensuring rail services are reliable and well-maintained, providing decent WiFi connections and proper power points is going to be crucial for a modern business that relies on travel.”