Analysis of information sources in references of the Wikipedia article "イギリスの首相の一覧" in Japanese language version.
All Prime Ministers ... were members of the Privy Council ... This means they are entitled to be addressed as 'The Right Honourable'.Locker-Lampson, Godfrey (1907年). A Consideration of the State of Ireland in the Nineteenth Century (英語). London, UK: Archibald Constable and Co. the Internet Archiveより。
The title ... was not used in an official document until 1878 when Disraeli ... signed the Treaty of Berlin as 'First Lord of the Treasury and Prime Minister of her Britannic Majesty'.
The title ... was not used in an official document until 1878 when Disraeli ... signed the Treaty of Berlin as 'First Lord of the Treasury and Prime Minister of her Britannic Majesty'.