Likely difficult to find proof or definitive examples of it happening, but Intelligence Services Act 1994[0] states: http://www.legislation.gov.uk/ukpga/1994/1

Likely difficult to find proof or definitive examples of it happening, but Intelligence Services Act 1994[0] states: http://www.legislation.gov.uk/ukpga/1994/13/section/3 http://www.legislation.gov.uk/ukpga/1994/13/section/3 > [GCHQ shall] monitor or interfere with electromagnetic, acoustic and other emissions and any equipment producing such emissions and to obtain and provide information derived from or related to such emissions or equipment and from encrypted material; [... said functions] shall be exercisable [...] in the interests of the economic well-being of the United Kingdom in relation to the actions or intentions of persons outside the British Islands There's very similar language for SIS. [0] http://www.legislation.gov.uk/ukpga/1994/13/section/3 http://www.legislation.gov.uk/ukpga/1994/13/section/3