The royal prerogative is in much use in the realm of foreign affairs . It is the monarch who recognise foreign states ( although several statutes regulate the immunities enjoyed by their heads and diplomatic representatives ) , issues declarations of war and peace , and form international treaties . The monarch also have the power to annex territory , as was done in 1955 with the island of Rockall . Once territory have been annexed , the monarch have complete discretion as to the extent to which the government will take over the former government 's liabilities ; this was confirmed in West Rand Central Gold Mining Company v The King . The monarch also have the power to alter British territorial waters and cede territory . Her freedom to do these things in practice is doubtful , in that they might deprive British citizens of their nationality and rights . When the island of Heligoland was ceded to Germany in 1890 , Parliamentary approval was first sought . The monarch can also regulate colonies and dependent territories by exercising the prerogative through Orders in Council . The courts have long fought against the monarch 's use of this power : in R ( Bancoult ) v Secretary of State for Foreign and Commonwealth Affairs ( No 2 ) , the Court of Appeal ruled that using Orders @-@ in @-@ Council to frustrate judicial rulings was an unlawful abuse of power , although this ruling was later overturned .