Counter-Terrorism and Security Bill

My Lords, on Amendment 2, can the noble Lord opposite explain whether there is any particular reason for choosing two years for the sunset clause, after which time, subject to an affirmative resolution, there would be a permanent continuation? What is the logic behind that two-year split? Why is there not, in a sense, a rolling sunset clause every two years? If there is a rationale to it, perhaps the noble Lord can explain the reason for that two-year review and then no more, as it were, apart from the normal rules that apply to primary legislation.