Sophisticated satellite systems are being blamed for the latest problem to hit Southern's state-of-the-art new trains.

Passengers have been left trapped in carriages because the technology has failed to recognise that their train has arrived at a station.

The doors only open if the satellite can pinpoint a train's exact location and the driver has safely lined up carriages on the platform.

But trains are arriving at some stations which are not recognised by the Global Positioning System (GPS).

When this happens, the train doors lock automatically for safety as the system assumes the train is still outside the station.

The driver then has to override the technology by manually opening the doors, causing a delay.

It is the latest fiasco for passengers on Southern's £850 million Electrostar train fleet, which has been beset with problems since it was introduced at the end of 2002.

One of the stations the satellite system is having trouble finding is Preston Park, Brighton.

Trains have arrived at the station and doors have failed to open prompting some passengers to force open the emergency doors to release themselves.

The rail company is gradually introducing Electrostar trains on all its routes in Sussex to replace the old slam-door stock.

Its satellite system was developed by the US military and relies on a series of global satellites.

Company spokesman Richard Lancaster said: "There has been a particular problem with the door functions on the new trains.

"They have a selective door opening system on board which takes a combination of GPS satellite signals to tell the train exactly which station it is located at and then ensure only the number of doors that are accommodated on the platform are opened.

"We have experienced a number of different problems which manifest themselves as the fleet grows and more new trains are introduced on differing routes.

"In some locations the GPS signal being received is of a much higher strength than the system it was designed for. This is being addressed by changes to the aerial on each train.

"Sometimes we have had problems with the train not locating itself and thus not opening the doors at all. In this instance the driver has to override the system by telling the train where it is and then giving a manual door release.

"In some instances this has not functioned at the first attempt and there have been delays while the driver tries to release the doors again. Reasons for this are being investigated.

"We have seen a pattern emerging of some individual trains being more prone to problems than others. This cannot be determined until they have been in service for several days or weeks and we are currently working closely with the manufacturers to fix these problems."