In a constitutional monarchy, the Sovereign acts according to constitutional rules, rather than arbitrarily. That is so even in a country such as Britain which has no codified constitution. Today the rules of constitutional monarchy whose purpose it is to preserve the political neutrality of the Sovereign, serve to protect her from political involvement. Her powers remain essentially residual - selection of a Prime Minister and refusal of a dissolution under very rare circumstances. The main influence of the Sovereign, however, comes through her exercise of the three rights identified by Bagehot - the right to be consulted, the right to encourage and the right to wam; and through her role as Head of the Commonwealth. The enormous popularity of the monarchy in Britain today arises because it has come to be divorced from partisan politics, and so can act as a focus of national unity.