South West Trains is considering the trains, already in use in Europe and the USA, for the busy Southampton to Waterloo line.

A major joint feasibility study between SWT and Railtrack is now under-way to look into the proposals, which are backed by passenger pressure groups.

In the last 18 months numbers of rail users have risen by a record 17 per cent, said Alan Shotter, spokesman for the Rail Users' Consultative Committee in the South-East.

"We need a long term solution, and we believe double-decker trains could be it," he said.

Experts say the increase is mainly due to economic growth creating new jobs in London, as well as motorists abandoning their cars because of road congestion on the M27, M3 and M25.

SWT spokeswoman Jane Lee agreed the service was stymied over increasing capac-ity. She said: "We're delighted more people are using trains but the growth is outstripping the extra services we are able to introduce.

"There are no easy solutions to this problem - we can only tinker at the edges.

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