Communications regulator Ofcom has handed out the maximum fine it can impose to Barclaycard for the "most serious and persistent" case of silent calls it has ever seen.

The credit card company was hit with a £50,000 fine after thousands of calls were made between October 2006 and May 2007.

The regulator refused to specify exactly how many calls were made but said it was substantially more than the 16,000 Abbey National was fined in similar circumstances.

"This is the most serious case of persistent misuse by making silent and abandoned calls that Ofcom has ever investigated," said Ofcom chief executive Ed Richards.

"Had we not been limited by the statutory maximum, we would have imposed a larger financial penalty to reflect this misuse."

A Barclaycard spokesman offered a full apology to those affected and said it had made "robust and lasting changes" to its processes to ensure future compliance.

Silent calls occur when an automated call centre dials a number and then transfers it on answer to an agent. But if no agent is available there will be no one on the end of the line for the customer.