LONDON (Reuters) - British cell phone retailer and telecoms operator Carphone Warehouse Group Plc (CPW.L) may have to pay up thousands of pounds in penalties for making "silent" calls that annoy customers, regulator Ofcom said on Friday.

Silent calls occur when automated calling systems at call centers generate more calls than the available call center agents can manage.

When the person called by the automated system answers the phone and there is no agent available, the system abandons the call and results in the person called experiencing silence on the line.

Ofcom, which has set a 3 percent daily limit for such calls, said Carphone and the three other companies -- Brakenbay Kitchens, Space Kitchens and IDT Direct or Toucan -- had persistently exceeded the limit.

"Between April and July 2006 all four companies' abandoned call rates regularly exceeded 3 percent and in some cases were higher than 20 percent," it said, adding that the companies had time until December 6 to present their cases to Ofcom.

"At this point Ofcom will decide in the case of each company whether to impose a financial penalty," it said.

The maximum penalty that may be imposed is 50,000 pounds ($95,000) per contravention, it said.