Fixed-term Parliaments Bill

Can the noble Lord explain my one reservation about a provision I otherwise support, which is about the point in the next Parliament when this option has to be exercised. Can it be exercised at any time through that Parliament, or does it have to be done early on? If it is not early on, is it fair that you do nothing for, say, two or three years, then when it looks as though you might quite like the protections of this Act, you decide in about the third year to revive it? Should there be some point at which you have got to place your bet?