The prospect of higher fares on public transport could have a devastating effect on London pollution levels, a report warns.

Against the background of a real increase in fares on buses and Tubes of up to 34 per cent in the past 10 years, the pressure group Transport 2000 has calculated the environmental cost of further rises. It has also looked at the damage of putting value-added tax on fares.

Lynn Sloman, its assistant director, said: 'A fares rise of 50 per cent would mean emission of an extra 185,000 tonnes of carbon dioxide a year in London alone.'

Another spin off would be increased private car use, reducing average speeds in the capital from 10.3 to 8.8mph during peak hours.

'We are not saying there will be a 50 per cent increase immediately. But looking at the signals the Government is giving, and what has been happening, it is reasonable to suggest you will see this sort of increase in real terms,' said Ms Sloman Since 1984, rail fares have increased in real terms by

22 per cent in London and 25 per cent in the South-east as a whole. London Underground fares have gone up 34 per cent and London buses 33 per cent.

London is the most expensive European city in which to travel with 10 commuter trips, each of six miles, costing pounds 15.65. That compares with pounds 10.45 in Amsterdam, pounds 8.80 in Paris and pounds 2.52 in Rome.

Transport 2000's research suggests a 17.5 per cent VAT fare increase would lead to a 6 per cent rise in carbon monoxide emissions in central London during peak periods and a 7 per cent increase in carbon dioxide emissions. A 50 per cent fare rise would bring an 11 per cent increase in carbon monoxide emissions and a 14 per cent carbon dioxide rise.

Researchers argue if VAT were imposed, London Transport would have to put up fares by 27 per cent overall to compensate for lost revenue as people switch to cheaper transport. Every 10 per cent increase in Underground fares leads one in 40 passengers to travel another way. A third of those use a car. A 10 per cent increase in bus fares means one in every 30 passengers transfers, a quarter of them to a car.

Ms Sloman dismissed Department of Transport claims that rail fares would not necessarily rise after privatisation. Ministers accept rail operators have a monopoly in London, so a cap on fare increases will be built into contracts.

Campaigners say higher fares will mean more cars entering London, increased traffic congestion, more stop-start journeys, and higher pollution levels.

A European Commission report into plans to put VAT on fares is due in the autumn.

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