London's rail chief has warned that overcrowding on the Capital's trains will reach third-world levels unless a programme of investment is put in place.

Peter Field said that economic growth will be slashed unless more money is put into public transport.

"The options for the nation are stark and simple - either suppress London's economic growth and face the consequences or invest in its rail infrastructure and the future prosperity of London and the UK," he said.

Field, the rail development director of London Rail, argued that priority should be given to investing in the Capital's tracks and rolling stock because of its strategic economic importance.

Unless the investment is put in place rail services in the South East will be approaching the standard of those in the developing world by 2011, he warned.

With demand for transport in London set to increase by 25 per cent by 2016, Field pointed to evidence suggesting that transport investment there provides better returns than anywhere else in the UK.

He called for faster progress on the east-west Crossrail line, the Thameslink 2000 project to improve capacity on north-south cross-London lines and on the westward extension of London Underground's East London line to Clapham Junction.

The total projected cost for the three initiatives is £15 billion.