That clause simply adds "make use of" to the beginning of the existing paragraph in the existing legislation[0]:

  (a)to 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; and

They're still bound by the second clause in it:

  (2)The functions referred to in subsection (1)(a) above shall be exercisable only—
    (a)in the interests of national security, with particular reference to the defence and foreign policies of Her Majesty’s Government in the United Kingdom; or
    (b)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; or
    (c)in support of the prevention or detection of serious crime.

[0] http://www.legislation.gov.uk/ukpga/1994/13/crossheading/gch...