Sybil was a cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

 living at 11

11 Downing Street

11 Downing Street , is the official residence of the Second Lord of the Treasury in Britain, who in modern times has always been the Chancellor of the Exchequer...

 and 10 Downing Street

10 Downing Street

10 Downing Street, colloquially known in the United Kingdom as "Number 10", is the headquarters of Her Majesty's Government and the official residence and office of the First Lord of the Treasury, who is now always the Prime Minister....

. Named after Sybil Fawlty

Sybil Fawlty

Sybil Fawlty is a fictional character from the BBC sitcom Fawlty Towers. She is played by Prunella Scales. Her age is listed as 34 years old as seen on her medical chart in the 1975 episode "The Germans", thus presumably indicating that she was born in 1941...

 from the TV show Fawlty Towers

Fawlty Towers

Fawlty Towers is a British sitcom produced by BBC Television and first broadcast on BBC2 in 1975. Twelve television program episodes were produced . The show was written by John Cleese and his then wife Connie Booth, both of whom played major characters...

, she was the pet of former Chancellor of the Exchequer

Chancellor of the Exchequer

The Chancellor of the Exchequer is the title held by the British Cabinet minister who is responsible for all economic and financial matters. Often simply called the Chancellor, the office-holder controls HM Treasury and plays a role akin to the posts of Minister of Finance or Secretary of the...

, Alistair Darling

Alistair Darling

Alistair Maclean Darling is a Scottish Labour Party politician who has been a Member of Parliament since 1987, currently for Edinburgh South West. He served as the Chancellor of the Exchequer from 2007 to 2010...

.

Confirmation of Sybil's tenure as Chief Mouser to the Cabinet Office

Chief Mouser to the Cabinet Office

The Chief Mouser to the Cabinet Office is the unofficial title of the official resident cat of the Prime Minister of the United Kingdom at 10 Downing Street. Only one cat, Humphrey, was given the title officially; the other cats are given this title affectionately, usually by the British press...

 was given on 11 September 2007 by Gordon Brown

Gordon Brown

James Gordon Brown is a British Labour Party politician who was the Prime Minister of the United Kingdom and Leader of the Labour Party from 2007 until 2010. He previously served as Chancellor of the Exchequer in the Labour Government from 1997 to 2007...

's official spokesman, who stated, "I understand the Darlings do have a cat, and the cat has recently been brought to Downing Street... The Prime Minister and Sarah do not have a problem with it. I am sure the cat will appear at some point".

Sybil, who was black and white, was the first cat at Downing Street

Downing Street

Downing Street in London, England has for over two hundred years housed the official residences of two of the most senior British cabinet ministers: the First Lord of the Treasury, an office now synonymous with that of Prime Minister of the United Kingdom, and the Second Lord of the Treasury, an...

 since Humphrey

Humphrey (cat)

Humphrey was a cat employed as the Chief Mouser to the Cabinet Office at 10 Downing Street, the official residence of the Prime Minister of the United Kingdom, from October 1989 to 13 November 1997...

 was reportedly removed in 1997 due to Cherie Blair

Cherie Blair

Cherie Blair , known professionally as Cherie Booth QC, is a British barrister working in the legal system of England and Wales. She is married to the former Prime Minister of the United Kingdom, Tony Blair; the couple have three sons and one daughter...

's aversion to cats.

Sybil failed to settle in Downing Street and there were rumours that Gordon Brown disliked her. She left Downing Street after six months and died in July 2009.