And the answer: Larry.
Outlasting David Cameron, Theresa May, and soon-to-be Boris Johnson’s tenures, Larry has captured a confirmed three mice since 2011. While he’s in the “tactical planning stages” of mousing, Larry’s other duties include “greeting guests to the house, inspecting security defenses, and testing antique furniture for napping quality.”
In the residence and executive office of the Prime Minister, there lives one fierce feline protector that the world sorely needs: Larry the cat. Although the United Kingdom’s current mouser may have enjoyed a long tenure in office, the history of cats on Downing Street dates back much further. Official records of Downing Street’s feline resident begin in 1929, but there is evidence of a cat in residence in the English government dating back to the 1500’s. During Henry VIII’s reign, Cardinal Thomas Wolsey placed his cat by his side while acting as Lord Chancellor. That means mice have likely been steering clear of Downing Street for around 500 years!
While the Chief Mouser might stalk the halls of the Prime Minister’s residence, the cat doesn’t technically belong to the Prime Minister, and it’s rare for a Mouser’s term to exactly coincide with the PM’s. As such, several cats (including the incumbent Larry) have held the position across many different political terms. The longest term served by a Chief Mouser was that of Wilberforce, who served under four different Prime Ministers: Edward Heath, Harold Wilson, Jim Callaghan, and Margaret Thatcher.
Larry is the first feline to receive the official title of Chief Mouser. In 2011, Larry was hired after several rats “[scurried] across the steps of Number 10 Downing Street for the second time during a TV news report," according to ITN. On February 14, 2011, it was reported that a cat named "Larry" had been brought in to address the problem.
Learn more about the history of Chief Mousers and beloved Larry here.