It will soon be goodbye to compartments, draughty slam-doors, buffet cars and, hopefully, smelly toilets as train operator South Central invests £850 million in new stock.

Passengers will travel in sleek, brightly-coloured Electrostar trains with computerised destination and information displays inside and out.

The new trains could even feature an airline-style service where passengers who have paid a premium rate are served drinks and snacks in their guaranteed seats.

However, the trains have already come in for criticism from the Rail Passenger Committee for Southern England, which is calling for design modifications.

The watchdog says there is not enough leg room between seats at the end of each carriage, there is a not enough space for heavy luggage and nowhere for cycles to be carried. It is also worried about lack of space for wheelchairs.

The first of the 700 carriages, which will eventually make up the entire South Central fleet, are beginning to role off the production line at the Bombardier works in Derby.

The order is one of the biggest made by a train company.

It has preserved jobs in Derby and will mean about 30 new posts at the Lovers' Walk depot in Brighton, where the fleet will be maintained.

South Central, which took over rail services from Connex in August last year, hopes its commitment to new stock will help win it a 20-year franchise to run services in central Sussex by the end of this year.

If that happens the company will call itself the New Southern Railway, harking back to the days of the Brighton Belle and green electric trains with sunshine-yellow lettering which ran on time.

The trains are undoubtedly incomparable with the decades-old stock in use today. But the shortage of leg room and the lack of space on luggage racks for anything bigger than a brief case or shopping bag will displease some travellers.

At the unveiling of the trains, so new that visitors had to wear covers on their shoes, it became clear the carriages were designed for short journeys as there is plenty of standing space next to the sliding doors.

Electronic boards with the names of stops flashing up will ensure travellers know how their journey is progressing.

The white tables will need frequent cleaning as will the blue seats and carpets if they are to remain respectable.

The trains are certainly quieter than their ageing predecessors, as a journey along the test track at Derby proved.

There should be no more freezing cold or uncomfortably hot journeys as a computerised heating system will maintain the temperature at a constant 21C (just under 70F).

The toilets, with hot and cold water, should be an improvement and some have baby changing facilities.

South Central managing director David Franks is convinced his trains will herald the start of a train travel revolution.

He said: "We want to raise the standard of rail travel and re-educate the public as to what rail travel is all about."

As for criticism of the new carriages, he said: "There is enough leg room for most people. Most of our traffic is commuter traffic and day-trip traffic.

"People who want to carry large cases can put them between the seats.

"Those travelling with larger luggage going to Gatwick can, of course, use the Gatwick Express. We are not the main carrier to Gatwick - ours is a different kind of market.

"There is room for cycles and wheelchairs."

The absence of first-class carriages does not worry the man who was once the youngest station manager at Brighton and commutes each day first class from Haywards Heath to Blackfriars.

He said: "We are looking at providing a first-class service for passengers who want to pay for something that will guarantee them a better style of travel.

"At the moment it is difficult to police first-class travel. When everyone bundles into a train at East Croydon, it is often impossible to prevent people going into first-class compartments.

"I have in mind a coach set aside for some form of premium service travel, say with a guaranteed seat, free newspaper and a coffee and snack service.

"I would be prepared to pay for that myself. There are too many people in the rail industry using up the first-class compartments.

"These new trains will enable us to provide a new style of service. I would like to go back to the days of the Brighton Belle.

"But first things first: Let us get our current stock and then these new trains running reliably during the next few years.

"Then we can concentrate on creating a New Southern Railway."