A company that plagued members of the public with 46m automated nuisance calls has been slapped with a £350,000 fine.
The Information Commissioner's Office (ICO) handed its largest ever fine to lead generation firm Prodial Ltd after more than 1,000 people complained about the calls, which played recorded messages relating to PPI claims.
Frustrated complainants said they were called repeatedly and often there was no opt-out option.
One person said they were left feeling helpless by the calls, which came at all times of day or night, and a doctor who fell victim to them said the constant calls were interfering with work as they had to answer them in case of emergency.
Information from the calls was used to sell people's personal details on to claims management companies, said the ICO, which can hand out fines of up to £500,000.
Companies are allowed to use internet phone lines to cheaply make large volumes of recorded marketing calls, but only to people who specifically consent to being contacted in this way.
According to the ICO, Prodial didn't have any such consent.
The Brighton-based company was operating out of a residential property and hiding its identity, which made it harder for people to report the calls
Information commissioner Christopher Graham dubbed the case "one of the worst cases of cold calling we have ever come across".
He said: "The volume of calls made in just a few months was staggering.
According to the ICO, the marketing campaign could have turned over nearly £1m, but the company has been put into voluntary liquidation by one of its directors, so the ICO's enforcement team is trying to get the fine from liquidators.
"This was a company that knew it was breaking the law. A company director admitted that once the ICO became involved, the company shut down.
"That stopped the calls, but we want to send a clear message to other firms that this type of law-breaking will not pay. That is why we have handed out our highest ever fine.
"No matter what companies do to try to avoid the law, we will find a way to act."
The landmark fine comes after Baroness Neville-Rolfe, minister for data protection and nuisance calls, called for nuisance calls to be treated as a form of harassment, rather than merely an "unfortunate by-product of the rapid growth in data-led marketing".
The government is looking at options for further regulation that will help fight the "scourge" of nuisance calls, she said.