Making an obscene, harassing or malicious telephone call may be a criminal offence under the Communications Act 2003 or under the Protection from Harassment Act 1997. If you receive such a call, you should report the matter to the police. The police can, for example, authorise the telephone service provider to trace malicious calls. A communications provider can override anything done to prevent the display of the identity of the caller where the person called has asked for nuisance or malicious calls to her/his number to be traced. If the person who is making the calls is prosecuted, you may have to give evidence in court. If you are receiving obscene or malicious phone calls, you could consider changing your phone number and getting an ex-directory number. The phone service provider may have procedures which deal with malicious, obscene or harassing phone calls. You need to check what provision the phone service provider's Code of Practice has for dealing with such calls. For example, BT has specially trained staff to help people to take action to solve the problem of malicious phone calls. A 24-hour recorded message tells them what to do if they need help - tel: 0800 666700.
Silent calls are normally caused by automated calling systems used in call centres. Ofcom guidelines state that call centres using these systems should play an information message if a call is abandoned. However, if you are still receiving silent calls, you should contact Ofcom if you know the name and number of the company concerned, or, if you are unable to identify the caller, you should contact your telephone service provider.
Almost all phone service providers supply a service called caller display or caller return. Caller display shows the number of the caller, provided the phone receiving the call has a visual display unit. Caller return enables someone to find out the number of the last caller by phoning 1471. Caller return may be of limited use in the case of malicious calls, as the person making the call can withhold her/his number by phoning 141 before making the call. However, in the case of nuisance or malicious calls, a number may be traced at the request of a subscriber even if the caller has concealed her/his number. Someone with a visual display unit can decide not to answer a call if the caller's number is not displayed.
It is unlawful to make unsolicited telephone calls for direct marketing purposes to any telephone subscriber who has registered with the Telephone Preference Service, or who has previously notified the caller that marketing calls should not be made on that line. It is also unlawful to transmit recorded communications for direct marketing purposes by means of an automated calling system, unless the subscriber has previously consented to these communications being sent. Complaints about direct marketing companies who continue to contact people registered with the Telephone and Fax Preference Services can be made to the relevant preference service, or to the Information Commissioner who has the power to take enforcement action in appropriate cases.
For further information, call into or telephone your local CAB.
Please note that this answer is correct as of November 2011