Our reporter received many calls from motorists who complained they had been wrongly fined sums of up to £120 - some had received multiple fines running into hundreds of pounds.

The findings come as a new study today highlights concerns over the economic effects of the charge.

We found that despite the millions being paid to Capita, many of its staff gave out inaccurate advice and struggled to understand the complexities of the charging system. One company manager even admitted to staff that working conditions have been "shit".

What is particularly shocking about our findings is that they come after the Mayor's assurances that Capita's "start-up" problems are now being eradicated. It is the second time the Evening Standard has investigated Capita. In the runup to the introduction of the controversial charge last February, our first investigation discovered confusion and panic in the charge call centre given the task of processing payment and handling complaints.

There was a backlog of applications, operators were dealing with calls after just half an hour's training and calls were taking twice as long as expected.

Mr Livingstone dismissed our findings at the time, but seven months later he admitted that he almost sacked Capita. The contract was renegotiated, with Capita promising higher-quality targets in return for an extra £31million.

But when we returned to the call centre in Coventry, things were arguably as bad as ever.

Capita's questionable attitude towards the public started during training, when recruits were told by a call centre manager that customer satisfaction "does not matter".

A female trainee told of one adviser who was asked by a caller to register 20 vehicles. He responded by just putting the phone down. "You didn't see that," he told the trainee. On other occasions they fob off callers with the excuse that someone will call them back - even though our reporter rarely saw this happen.

To keep up with the volume of calls, staff were also overworked. One trainee saw an adviser in the last hour of his 12-hour shift who was being begged by his team leader to stay for another five hours. "I think he didn't even know his own name," said the trainee.

The result is that the system is plagued with thousands of minor errors - any one of which can lead to a series of wrongly issued fines and months of aggravation for customers. During training, recruits were told there are 14,000 duplicate entries "clogging up" the system - a claim dismissed as "historic" by Capita.

A newsletter at the end of October revealed that the "accuracy level" for information given out by advisers was 46 per cent; in other words, more than half the calls had advisers telling callers something wrong, or not telling them something they were supposed to.

Although there was an improvement during the five weeks our reporter was under cover, as new staff boosted numbers, there were still concerns about the service.

Perhaps the definitive view came from a new recruit who had several years' experience in customer services when he started at Capita. He left after only two weeks, calling the company's standards "rubbish".

When the Evening Standard presented Capita with our findings, the company insisted it was "extremely rare" for any operator to hang up on a call, saying this would only happen if a customer became abusive. The company added that there is a system in place to attempt to return calls.

The company denied that recruits were ever told customer satisfaction "does not matter" and said greater emphasis is now placed on "quality" during training.

Capita added: "The allegation of deliberately massaging down complaints numbers is strenuously denied. Capita takes complaints very seriously."

A spokesperson for Transport for London said: "The inevitable glitches of such a major new scheme are addressed by TfL's tough performance regime, which imposes large financial penalties upon Capita if improved performance targets are not met."

Meanwhile, a quarter of retailers inside the charge zone say they have had to lay off staff as a direct result of the charge, with only two per cent recruiting new employees.

Today's survey of 334 firms, by the London Chamber of Commerce, shows that 79 per cent of businesses are recording lower takings compared to a year ago.

Colin Stanbridge, chief executive of the London Chamber of Commerce, said: "Any move to extend the zone beyond its current boundaries would be folly until these problems have been addressed."