Overcrowding will worsen on several of Britain's busiest rail lines because the Government has quietly cancelled plans for more than 300 additional carriages.

Southern and South Eastern, two of the largest commuter franchises, are likely to bear the brunt. The Government will save about £70 million a year from the decision, which reverses a commitment in the rail White Paper published in July 2007.

The network's most overcrowded trains have more than 70 people standing for every 100 sitting, according to Department for Transport figures released under the Freedom of Information Act.

The 7.15am from Cambridge to King's Cross carries an average of 870 people but has only 494 seats. The 8.02am from Woking to Waterloo carries 865 and has 492 seats. Passenger groups criticised the White Paper for promising only 1,300 new carriages by 2014, an increase of about 13 per cent, despite forecasting a 22.5 per cent rise in rail journeys. They said that the extra carriages would fail to keep pace with demand, much less alleviate the high level of overcrowding.

However, the Government has decided to reduce its commitment from 1,300 to fewer than 1,000 carriages. In answers to parliamentary questions posed by the Conservatives, Paul Clark, the junior Transport Minister, said that only 423 carriages had been ordered. The Government expects to order another 550 carriages over the next two years, leaving the network 327 carriages short of the original commitment.

Theresa Villiers, the Shadow Transport Secretary, said: “Three consecutive transport secretaries have promised these extra carriages, and now it turns out to be a con. With passengers struggling with sub-cattle-class overcrowding and sky-high fares, the least they can ask is for Labour to live up to its claims on extra carriages.”

Bruce Williamson, spokesman for Railfuture, the passenger lobby group, said: “It is ludicrous for the Government to cut back on what it promised. Rail carriages are a long-term investment and it would be short-sighted to argue that the current reduction in the rate of passenger growth means these carriages are not needed. By the time these trains are delivered, the recession will probably be over and high rates of growth will have resumed.”

The DfT said that it would seek to make up the shortfall by purchasing carriages for the Thameslink route. However, the Government previously stated that carriages ordered for the Thameslink upgrade, due by 2015, were a separate commitment and would not count towards the 1,300 carriages promised in the White Paper. Last June Tom Harris, then the Rail Minister, said that “1,300 carriages will be added to the fleet. These are net additions, not replacements, and don't include the 1,100 new carriages for Thameslink routes.”

The average age of trains on regional routes has risen to 18 years, the highest for seven years, according to the Office of Rail Regulation. On long-distance routes some trains are more than 35 years old.

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