About 150 people gathered in Trafalgar Square, central London, to urge the government to force Railtrack to instal the £1bn Automatic Train Protection (ATP) system.

Experts believe ATP could have prevented both disasters.

Tony Cima, 46, from Stroud, Gloucestershire, who attended the rally, survived the Paddington crash last month. He said he still had awful memories of the accident.

"The worst thing was being unable to help people, I could have done more for them," he said. "ATP is the only way of getting the drivers to stop. We don't want a cheapskate alternative."

Campaigners want better rail warning systems

Addressing the gathering, London mayoral hopeful Ken Livingstone said: "The more you look at Railtrack's involvement in the railways, the more it looks like a gravy train for its investors and less like a modern integrated train service for the public."

Liberal Democrat mayoral candidate Susan Kramer said: "It is political leadership that has been lacking in making sure we have safer trains. Britain should have the best safety system in the world."

Earlier it was announced that the public inquiries into the two rail disasters are to hold a number of joint sessions on common issues.

The BBC's John McIntyre reports: "Feelings of anger and frustration are clearly undiminished"

The arrangements have been agreed between the chairmen of the two inquiries, Professor John Uff and Lord Cullen, and the Deputy Prime Minister, John Prescott.

The Health and Safety Commission said that while the major parts of the two inquiries will be conducted separately, the chairmen will sit jointly to hear evidence on Train Protection and Warning systems, the future application of Automatic Train Protection, and trains passing signals at danger.

Thirty-one people died in the Paddington crash, the country's worst rail disaster for more than 10 years, while seven people died at Southall in 1997.

At the Southall inquiry on Friday, Britain's chief inspector of railways, Vic Coleman, told how he urged train operators to introduce speed restrictions within days of the Southall rail crash.

Mr Coleman said he also wrote to the 25 train-operating companies setting out the benefits of having a second person in the driver's cab helping to observe signals.