A new train broke down this morning, sparking commuter chaos during the rush hour.

The train is one of South Central's £856 million fleet of Electrostar 377s, dubbed "the birth of a new era in rail travel" by managing director David Franks.

Last month one broke down on the way to Seaford just hours after it was unveiled to the public. And the introduction of the new stock had to delayed for three months after test runs showed problems with the door operating system.

Today, services from Seaford to Newhaven Harbour were halted after the train broke down at Bishopstone, near Seaford, blocking the single track line.

Commuter Yvonne Shooter, from Seaford, was due to catch the train to Lewes from Seaford station when she was told at 8.05am the service was delayed.

She said: "It's a single track and if one train breaks down nothing can get through either way."

Passengers were told the problem was to do with the train's brakes and frustrated commuters, who pay £115 a month for a season ticket between Seaford and Haywards Heath, demanded buses be laid on.

Ms Shooter, who works for Zenith Insurance, Haywards Heath, had to drive to work.

She said: "It's a very busy station. There were at least 50 people waiting."

A spokesman for South Central said the cause of the breakdown was still being investigated.

The trains are equipped with air conditioned carriages and sliding doors. South Central hopes to replace its entire stock with the new trains by the end of 2004.