Deputy Prime Minister of the United Kingdom

The deputy prime minister of the United Kingdom is an honorific title given to a minister of the Crown and a member of the British Cabinet, normally to signify a very senior minister, the deputy leader of the governing party, or a key political ally of the prime minister. It does not entail any specific legal or constitutional responsibilities, though the holder will normally be assigned some duties by the prime minister and in recent times this has typically always included deputising for the prime minister in the House of Commons, domestically and abroad.

Source: Wikipedia — Deputy Prime Minister of the United Kingdom (CC BY-SA 4.0)