 British passports are also issued under the prerogative , though these are also covered by statute law . Under the common law , citizens have the right freely to leave and enter the United Kingdom . In R v Foreign Secretary ex parte Everett , the courts held that it was their right to review the granting of passports to , and the <unk> of passports from , British citizens . The writ of ne <unk> <unk> is also used to prevent a person leaving the country . The right to make treaties is a disputed prerogative power : under Blackstone 's definition , a prerogative power must be one unique to the monarch . 
