In a sign that the UK is already in recession, fewer car and lorry journeys on motorways, rural and urban roads were made over the last six months compared to the same period a year ago. Traffic on Britain’s roads is decreasing significantly for the first time since the three-day week of the early 1970s, suggesting the car economy is heading for a crash, official figures revealed yesterday.

The Department for Transport (DfT) recorded two consecutive quarters where road traffic has decreased year on year – the first time for more than 30 years. If the trend continues to the end of the year, it will hugely undermine the “great car economy” championed by Margaret Thatcher.

Sales of new cars have fallen by 23 per cent and are at their lowest since 1996. The motor industry is suffering across the world, with Volvo, the Swedish giant, selling just 115 heavy trucks over the past few months, compared to 41,970 during the same period last year – a 99.7 per cent fall!

The jobs of 3,700 people at two UK car plants are at risk after General Motors warned it would be bankrupt within months unless it received a bailout from the US government.

The new traffic figures emerged as the UK Government prepares to announce car-related tax cuts as part of the Prime Minister Gordon Brown’s strategy to get Britain through the recession. Planned vehicle excise duty increases for older cars are expected to be scrapped, while ministers are examining plans by the German government for tax reductions on green vehicles. On Friday the Prime Minister said he would work with other EU leaders on fiscal policy to support economic growth – a signal that tax cuts to reinvigorate the economy are being considered.

As Mr Brown and the Conservative leader, David Cameron, battle it out over the economy, a poll today puts the Conservatives 13 points ahead of Labour. The ICM survey for The Sunday Telegraph suggests that despite Labour’s surprise win in the Glenrothes by-election, the “Brown bounce” could be short-lived.

Besides the three-day week in 1973 and two world wars, traffic has steadily increased since the beginning of mass production of the motor car more than a century ago. But the new DfT figures show a 2.2 per cent decrease between July and September this year. This followed a 0.5 per cent decrease between April and June. The decline runs against the official predicted trend of an increase in traffic of 1-2 per cent a year.

Traffic congestion has also decreased on motorways and A-roads. The average vehicle delay on the slowest 10 per cent of journeys was 3.67 minutes, down from 3.95 minutes for the year ending September 2008.

Britain is in the early stages of a recession, with unemployment rising and industry shrinking, leading to fewer cars and HGVs on the roads. But during the recession of the 1990s, traffic remained static, suggesting there are other reasons for the decline.

It would appear thousands of motorists are giving up driving, either because of soaring fuel costs, rising parking and car taxes or because of the environmental cost.

Tony Bosworth of Friends of the Earth said: “The Government must help people to use their cars less – and tackle climate change – by giving them better public transport alternatives, and making it safer and easier to cycle and walk.”

When she was Prime Minister, Margaret Thatcher hailed the car-based economy as the ultimate expression of the individual over the state. In the 1980s and 1990s, road traffic rose substantially from 215 billion vehicle kilometres in the year 1980 to 378.7 billion in 2000. Last year traffic reached 513 billion vehicle kilometres.

Car ownership has steadily increased over the past decade, with the proportion of households in Britain without access to a car falling from 30 per cent in 1997 to 25 per cent in 2007. Homes with two or more cars outnumber those with no cars, increasing from 25 per cent to 32 per cent.

Road transport produces around a quarter of carbon dioxide emissions. Nearly 60 per cent of this is from cars. This summer petrol reached 118p a litre, but many retailers have since lowered this to below £1 a litre after criticism from the Prime Minister.