They should have been pensioned off by the end of this year, but old slam-door trains look likely to be a feature of our railways well into 2005.

Three firms which operate across Sussex have applied for permission to continue running the trains until next summer.

It is not the first time the deadline for replacing them with multi-million pound modern carriages has been put back.

South Central, which operates the Brighton to London service and coastal routes in Sussex, has spent millions on new trains but was forced to mothball many because there was not enough power in the tracks to use them all at once.

Essential upgrades put the December 2004 deadline out of reach.

Despite an extensive replacement programme, mainly with new Electrostar and Desiro trains, three rail companies - South Central, South Eastern and South West Trains - have asked the Strategic Rail Authority (SRA) if they can continue running slam-door trains until summer 2005.

If the SRA says yes, it will mean 560 of the old carriages will be allowed to remain in service throughout the South of England, with the last one removed by the end of June next year.

South Central has ordered 700 new Electrostar carriages.

They are gradually being introduced throughout the network.

Spokesman Matt Ball said: "This is purely an administrative move to enable us to continue running slam-door trains in Sussex if we have to.

"We hope to have Electrostar units making up the majority of services on all our routes by the end of this year. We may need to continue to run slam-door trains on the lines to Eastbourne and through West Sussex via Arundel into 2005.

"We definitely hope they will all be phased out by the summer of 2005.

"The majority of services on the Brighton Line and along the Sussex Coast are now operated by Electrostar units."

Shelley Atlas, of the Brighton Line Commuters, said: "We hope the old slam-door trains will be replaced on all routes as quickly as possible. They are dangerous and trains are frequently delayed at stations with people jumping on at the last moment."

Strategic Rail Authority chairman Richard Bowker said: "The new timetable gives an accurate forecast of when the entire fleet of Electrostar and Desiro trains are expected to be in service.

"But it is essential all parties involved in this project continue to work together to complete this programme as soon as possible "So far, more than 650 new carriages have come into operation on the southern England network and more than 350 Mark 1 carriages have been removed.

"Ironically, a number of the new trains have proved far less reliable than the old slam-door ones, which, although often dirty and overcrowded, are far less prone to breakdowns."