The true extent of the British love of furry animals and the Civil Service's obsession with keeping records became clear on Tuesday.
Humphrey, a former stray, left No 10 in 1997
Papers on the history of the official Home Office cat were among 50,000 files delivered to the National Archives.
A series of cats from a humble mouser in 1929 to a pedigree feline who could not be sacked for "diplomatic" reasons have been employed.
The files were handed over under the Freedom of Information Act.
The records start in 1929 with a request for a penny a day from petty cash to feed the office cat .
After the cat, now known as Peter, had to be put down at the age of 17 in 1946, he was replaced by Peter II.
But he was run over in Whitehall and also had to be put down.
He was replaced two months later by another kitten called Peter, who shot to stardom after appearing on BBC's Tonight programme in 1958.
In March 1964, at the age of 16, Peter succumbed to a liver infection and had to be put down.
As a replacement, the Lieutenant Governor of the Isle Man, Sir Ronald Garvey, sent one of the island's pedigree Manx cats - famous for their lack of tails.
The female kitten was named Peta in honour of her male predecessors.
When staff complained she was not toilet trained and lazy and suggested she might be "put out to grass", a memo was issued ordering she must remain.
Her appointment had been so public that she had gained "diplomatic status" and letting her go could result in adverse publicity, a memo from 1969 said.
There is no further mention of Peta until 1976 when the reply to an inquiry from a member of the public revealed she had retired to the country home of a member of staff.