The taxman could be making as many as 300,000 "nuisance" telephone calls a year, an MP has claimed.
Ofcom says silent calls cause 'anxiety'
The menacing "silent calls" are made by automated dialling systems used by the tax collectors to chase late payments.
But Lib Dem MP John Hemming says the practice must end and warns Customs and Revenue it risk fines of up to £50,000 a call under new rules.
Paymaster General Dawn Primarolo said Customs and Revenue was "considering" the new guidelines.
Silent calls happen when companies use automatic dialling machines to ring several people, but then only speak to the one who answers first.
The communications regulator, Ofcom, wants companies to leave recorded messages, stating who they are and why they have called.
Earlier this month, the government backed a tenfold increase - to a maximum of £50,000 - in fines for silent calls.
"Consumers deserve proper protection," said Trade and Industry Secretary Alan Johnson.
"We are showing how determined we are to crack down on the distress nuisance calls cause the public."
Most silent calls are made by commercial organisations but Ofcom says "those parts of government whose business involves making large volumes of telephone calls may also be making silent calls".
The Inland Revenue, as the agency was called before its merger with HM Customs, made 7.5m calls using predictive dialling in 2004/05 but Miss Primarolo said in a Commons written answer "full information is not known" on how many of those were silent.
Mr Hemming said the figure could be as many 300,000, based on "industry standard" figures from the Direct Marketing Association.
He said "They (the government) do not want to admit that they contribute to the many millions of times that people are disrupted and caused anxiety by 'silent calls'. "Ofcom produced new guidelines on 31st October, but the tax man is still "considering" Ofcom's guidelines.
"It is quite clear that the taxman is responsible for 'persistent nuisance' and could be liable to fines of £50,000. A fine of £50,000 for each of the 300,000 calls would be £15bn.
"I am surprised that the taxman believes that following the law is optional."
In a written parliamentary answer, Ms Primarolo said: "HM Revenue and Customs was created as a legal entity on 7 April 2005. Of the two former departments, HM Customs and Excise did not make use of predictive diallers during this period.
"It is estimated that the Inland Revenue - and contractors acting on its behalf - made around 7.5m calls using predictive diallers during 2004/05. Full information is not available on the number of calls where contact was made but operators were not available.
"HMRC is considering Ofcom's latest policy and guidance on silent calls alongside the associated Ofcom Consultation Document which was published on 31 October."
BT reports that it currently handles about 80,000 complaints a month about silent calls.