At present, there is no satisfactory means of restraining a Government from introducing invasive measures into the law. As we saw with the last Government, Parliament seems unable or unwilling to control many outrageous intrusions into our established civil liberties. Any Government has a tendency to believe that security (including strong laws controlling individuals) is more important than individual freedom. The last Government carried this tendency into mania. A written constitution would at least allow laws to be scrutinised by the courts in accordance with principles settled in advance.
It would be a good idea to have a written constitution to replace our flexible but uncertain rules which hardly provide any constraint on Government action.