The flash of a speed camera has become one of the main irritants for motorists across Britain. But the consequences of being caught depend on where in the country you are, figures from the Department for Transport show.

In some areas, such as Cheshire, Hertfordshire and Kent, nearly every offender caught on camera will be traced but in London and Manchester half of drivers escape fines and points on their licence.

The department said the figures were not taken over a sufficiently long period to be representative, but furious motorist groups called for greater consistency after the accounts of 35 safety-camera partnerships showed huge regional discrepancies.

An RAC spokesman said: "You could be driving through one county where prosecution rates are high, but in another the message could be very different. Number-plate cloning or failure to update registration details are also problems that affect the figures. Some forces offer speed awareness courses instead of points on a licence."

The road safety pressure group Brake, which backs the use of cameras, said the problem needed investigating. "It's a little worrying that the figures are so low in some areas," a spokeswoman said. "There needs to be a reasonable consistency for drivers across the country. People who speed need to know that there's a reasonable chance they can be caught and, if they are caught, they are going to be prosecuted."

Paul Smith, founder of the SafeSpeed road safety campaign, opposes the use of speed cameras and believes they inadvertently encourage an "untraceable motoring underclass".He said: "Camera and computer enforcement of speed fines encourages people not to register their cars properly, so a huge number of vehicles are untraceable. There is no alternative to policing the roads if we want them to be safe. The factors causing these disparities include a large number of unregistered vehicles in areas such as Manchester and London."

In Greater Manchester, only 53 per cent of those caught received fixed penalty notices, while in the West Midlands the proportion was 59 per cent. London had the worst rate - only 46 per cent of offenders were fined in the capital.

In South Yorkshire, almost one-quarter escaped fines despite being warned of intended prosecution. But in West Yorkshire, every culprit was punished. Other partnerships to act against 100 per cent of motorists were Bedfordshire and Luton, Humberside and West Mercia. Gloucestershire, along with Avon and Somerset, had a 57 per cent prosecution rate; in Essex it was 58 per cent.