The AA has warned that London's traffic congestion charging system could be undermined by muddy number plates, bad weather and inaccurate data.

Capita won the £230m, five-year contract from Transport for London (TfL) to provide the infrastructure. Some 700 cameras will capture number plates for cross-referencing with a central database of all drivers who have paid the £5 charge. Vehicle owners will be sent a penalty notice if they fail to pay by midnight each day.

The process is relatively simple, but external factors such as weather conditions, cars following each other too closely, or dirty number plates, could cause serious problems, says AA head of roads and transport policy Paul Watters.

'TfL will not take chances with enforcements and will probably throw away a number of potential penalties rather than expose the fact that the technology they have spent a lot of money on is not 100 per cent reliable. It's the right policy but we will never know the extent that happens,' he said.

Other potential problems include penalties being sent to the wrong people, payment information not reaching the database fast enough to stop penalties being sent out, and fines being incurred by the one in ten London vehicles not correctly registered, says Watters.

'We don't have a lot of faith the testing will have ironed all the problems because we have seen debacles before with this type of project,' he said.

TfL says obscured number plates will not be a problem because the system uses an infra-red flash to read the number underneath any surface material.

'Everything has gone entirely to plan and we are very confident Capita can deliver and run the systems,' said a TfL spokesman.

The charge will come into effect on 17 February.