Telecoms giants BT and Vodafone have insisted they do not reveal customers' data unless required by law, in the wake of reports that they handed over information to eavesdropping agency GCHQ.
Documents said to have been leaked by whistleblower Edward Snowden apparently show that a number of telecoms companies allowed GCHQ access to undersea cables which carry their phone and internet traffic, allowing them to see details of customers' phone calls and email conversations.
Names of the firms, also said to include US-based Verizon, were revealed by Germany's Suddeutsche newspaper which claimed to have details of a spy programme, codenamed Tempora, which allows GCHQ to tap into fibreoptic cables and store data.
Suddeutsche reported that internal papers from GCHQ from 2009 showed the companies - some of which were given codenames - including Verizon Business (known as Dacron), BT (Remedy), and Vodafone Cable (Gerontic), as well as Global Crossing, Level 3, Viatel, and Interoute.
The reports are the latest in a series of claims prompting public concern over "snooping" by intelligence agencies in both the US and UK. Other documents released by Mr Snowden revealed that the US National Security Agency (NSA) paid £100 million to GCHQ over the last three years to access and influence British intelligence-gathering, The Guardian reported earlier this week.
Although an inquiry by the Intelligence and Security Committee has found GCHQ did not use the US internet monitoring programme to circumvent UK laws, its chair, Sir Malcolm Rifkind, said it would mount a wider investigation into the legislative framework governing the intercept of communications.
In the wake of the claims concerning telecoms companies, both BT and Vodafone said today that questions relating to national security were for governments, not telecommunications providers, and that they did disclose any customer data unless required to by law.
A spokesman for BT said: "Questions relating to national security are for governments, not telecommunications providers. Having said that, we can reassure customers that we comply with the law wherever we operate and do not disclose customer data in any jurisdiction unless legally required to do so."
A Vodafone spokesman said: "Media reports on these matters have demonstrated a misunderstanding of the basic facts of European, German and UK legislation and of the legal obligations set out within every telecommunications operator's licence, in Germany and beyond.
"Cables carrying international communications traffic pass through multiple jurisdictions. Within the European Union, the legal protections and obligations with regards to those communications are defined under relevant EU legislation (as well as the European Convention on Human Rights) which is in force across EU member states, including Germany and the UK. Vodafone complies with the law in all of our countries of operation, including - in the case of our European businesses - the EU Privacy Directive and EU Data Retention Directive."