The trains will be phased in over the next year

Portchester platform is four-and-a-half metres too short for the Desiro trains, which are to be introduced next month.

The Strategic Rail Authority says it would cost �750,000 to extend the platform, and it would not get enough use to justify the expense.

Passenger groups say the problem should have been foreseen and tackled by now.

Again we see passengers bearing the brunt of the industry's problems Tim Nicholson Rail Passengers Committee Chairman

At present there are 15 direct trains a day from Portchester to London.

The Desiro trains are to completely replace South West Trains' fleet of slam-door trains over the next year.

The SRA say expanding the platform would involve moving power cables and re-siting signals, at huge cost to the taxpayer.

Slam-door trains avoided the problem by keeping one set of doors closed, but safety inspectors want to avoid that happening with the new fleet of trains.

Tim Nicholson, chairman of the Rail Passengers Committee, said he did not understand why the problem had not been anticipated.

"It's a fairly typical example of the un-joined up rail industry we have in this country and again we see passengers bearing the brunt of the industry's problems," he said.