Commuters stuck on the train from Brighton to London will soon be able to fire off an email to their boss or surf the web.

The world's first moving high-speed broadband internet connection has been installed on trains on the Brighton line.

In specially designated carriages anyone with a device that can use wi-fi, which is standard on most new laptops, will be able to connect to the internet.

For £5 an hour, commuters will be able to use a service that can even work in tunnels.

It is being installed by a partnership between T-Mobile, Southern Trains and Nomad Digital, which is providing the technology.

Three carriages, each seating about 70 people, have already been fitted with the wi-fi service, known as T-Mobile HotSpot, ready for the launch at the beginning of March.

A free trial will be offered in March and April. The service will also be available at train stations on the route.

It is hoped that by the summer, 14 of the new Electrostar trains from Brighton to London Victoria will be able to provide passengers with broadband.

The 55-minute route was chosen because it is heavily used by business people, with 8,000 commuters travelling each day.

All they will need is a laptop with wi-fi technology and a credit card. There may also be vouchers on sale.

If the system is a success, it will be rolled out to other Southern Trains areas in Sussex, Surrey, Kent, Hampshire and London.

Jay Saw, T-Mobile UK's HotSpot manager, said: "We think it's going to transform what people do on the train. The ability to get fast internet is pretty compelling when you try it yourself."

Brian McBride, managing director of T-Mobile UK, said: "We see a growing trend for business users needing to access email securely on the move."

Vince Lucas, Southern's commercial director, said: "This is another project that will help in our delivery of a modern and reliable train service."

Nigel Wallbridge, Nomad Digital's executive chairman, said: "We have proved it is possible without building towers or other costly infrastructure and customers should not experience a drop in service."

The wi-fi service uses 20 to 30 base stations along the route.

T-Mobile already provides broadband wi-fi access in stationary locations across the UK, such as coffee shops and hotels.

Those buying access for use on trains will also be able to use the net in these other HotSpot locations. Prices are likely to be £5 an hour, £7.50 for three hours, £13 for 24 hours, £30 a week or £45 for a monthly pass.