The European justice chief has fired a warning shot at Britain, following revelations that U.S. and U.K. spy agencies have developed capabilities to access personal information through smartphone apps such as Angry Birds.

Viviane Reding, the European Union justice commissioner, said that if reports of spies storing personal data from fibre optic cables inappropriately were true, she would take action against the country.

"Where there is no link to EU law, national security is an area of Member State competence. The hands of the Commission are tied," Reding said in a speech at the Centre for European Policy Studies in Brussels on Tuesday.

"But let me be clear. If I come across a single email, a single piece of evidence that the TEMPORA program (the U.K.'s electronic surveillance program) is not used purely for national security purposes, I will launch infringement proceedings. The mass collection of personal data is unacceptable."

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She added that when she spoke to the U.K. about the nature of their surveillance programme, "the response was short: hands off, this is national security."