Motorists from rich areas could be charged more for road tolls in new 'pay-as-you-drive' postcode lottery

Car owners from wealthier districts could find themselves paying more than those from poorer areas.

A 300-page document issued to firms bidding to run road-pricing trials says any scheme must take account of 'fairness' and different 'road user classes'.

Motorists face a postcode lottery of 'pay-as-you-drive' road tolls if new Government plans are introduced

The pay-as-you-drive charges of up to £1.50 a mile would be based on a motorist's address on the electoral register.

A Department for Transport spokesman said differential charging was aimed only at allowing councils to offer discounts to residents.

But experts from the magazine Autocar said their analysis of the tender document suggested the middle classes would be in line for higher tolls.

'This opens the way for a postcode lottery of road-pricing charges.' said Hilton Holloway, associate editor of Autocar.

'It has all the potential for yet another stealth tax on Middle Britain.

'Using the electoral register to determine a driver's address makes it possible for ministers or councils to charge drivers from wealthier, well-heeled areas more than those in what they may consider to be more socially deprived areas.

'It's bringing class politics to pay-asyou-drive tolls. Ministers have decided to try to implement the world's most complex toll system.'

Drivers taking part in the trials, which would require 'spy in the sky' satellite technology, are expected be issued with windscreen-mounted charge cards.

Fees would vary according to the time of day.

Possible 'user classes' include blue badge holders and emergency workers.

The official document also defines the four main categories of road as city centre, city, country and countryside.

Vehicles would be assigned into one of seven classes, from motorcycles to HGVs.

Ministers also want the trials to test 'entry and exit' tolls which charge drivers for entering designated areas.

The document from the DfT's road pricing framework division was sent to firms interested in running eight feasibility trials. Lasting 24 months, these exercises will include a practical trial using 'real' money.

Ministers are close to signing contracts with four companies for the project to start in early 2010.

Tracking and charging devices will be fitted to about 100 cars.

The launch might clash with the next general election, making road-charging a political issue in marginal Labour constituencies  -  including Transport Secretary Ruth Kelly's in Bolton.

The DfT spokesman said of the 'user class' condition: 'This is intended purely to allow local authorities to offer a local residents' discount as part of any congestion charging scheme they chose to introduce  -  such as in London where residents living within the charging zone receive a 90 per cent discount.

'The technology trials will help local authorities with their thinking on congestion charging.

'We have been absolutely clear that we are a long way from being able to make any decision on national road pricing and that the legitimate concerns that people may have must be addressed first.'