The interception, recording and monitoring of telephone calls is governed by a number of different pieces of UK legislation. The requirements of all relevant legislation must be complied with. The main ones are:
Regulation of Investigatory Powers Act 2000 ("RIPA")
Telecommunications (Lawful Business Practice)(Interception of Communications) Regulations 2000 ("LBP Regulations")
Data Protection Act 1998
Telecommunications (Data Protection and Privacy) Regulations 1999
Human Rights Act 1998
The interception of telecommunications such as telephone calls and emails and of postal communications can potentially be a very severe intrusion into your privacy. Article 8 of the Convention, which guarantees your right to respect for your privacy, also expressly protects your right to respect for your correspondence, and correspondence can include telecommunications. For this reason the law strictly regulates the circumstances in which your post or telecommunications can be intercepted or monitored. Any interception which is not done in accordance with the law and which cannot be justified as being necessary and proportionate for a legitimate aim is likely to constitute a breach of your human rights.
Regulation of telephone tapping and other forms of interception of communications is governed by the Regulation of Investigatory Powers Act 2000, known as RIPA.
It is an offence for any person intentionally, and without lawful authority, to intercept any communication in the course of its transmission through a public telecommunication system and – except in specified circumstances – through a private telecommunication system . This offence is established under the Regulation of Investigatory Powers Act 2000 (RIPA). So it will be unlawful for a person to intercept, for instance, a telephone call though a landline, a call or text message through a mobile network, an email or message sent though the internet. This offence does not apply to stored communications, however, such as automatically recorded calls or messages on answering machines.
http://www2.law.ox.ac.uk/opbp/OPBP Intercept Evidence Report.pdf