As David Cameron prepares to move into No.10 Downing Street, a vastly more important British civil service post has yet to be filled. That, of course, is chief mouser to the cabinet office: the resident Downing Street cat.

Anecdotally, cats have been part of British governance since the time of Henry VIII. Unlike Kevin Rudd’s much-documented pets (check out this awww-worthy pic of Abby at the Million Paws Walk) or the various animal tenants of the White House, Downing Street’s cats do not belong to the incumbent prime minister but are on the Civil Service payroll as mousers.

Perhaps the most devious was Treasury Bill, who in 1924 used his feline wiles to squeeze a pay rise from the notoriously tight-fisted Philip Snowden, Chancellor of the Exchequer.

According to a 1936 account, Treasury secretary Sir Warren Fisher noticed Bill looking “thin and languid” and appealed to spend more on his food, but after giving “careful consideration to the case” the Lords of the Treasury declined. That’s when Bill slipped into Snowden’s office and made himself generally adorable. Snowden immediately noted: “Treasury vote: approve increase in cat’s pay.”

However, the first officially documented bureaucat was Peter; Home Office records from 1929 request a penny a day to feed him. He survived the Depression and the Blitz, and was put down in 1946 at 17.

His successor, Peter II, was prematurely run over in Whitehall; but Peter III became a media star after appearing on BBC’s Tonight show in 1958. Aged 16, he died of a bung liver in 1964.

Controversy dogged his replacement Peta, a female pedigree Manx cat. Staff tried to oust her in 1969, claiming she was lazy and incontinent, but fearing a public backlash, Downing Street mandarins granted Peta “diplomatic status”. She ended her days about 1978 on a civil servant’s country estate.

Wilberforce had the distinction of serving under four prime ministers from 1970 to 1988: Edward Heath, Harold Wilson, Jim Callaghan and Margaret Thatcher. Ever the economic rationalist, the Iron Lady saw Wilberforce as a cheaper option than a human pest exterminator.

Her asthmatic press secretary, Sir Bernard Ingham, recalled wheezy Monday mornings after Wilberforce had spent the weekend napping on his desk. He also revealed that Thatcher had bought Wilberforce a tin of sardines from a Moscow supermarket.

But the real star of British politics was Humphrey. Proving worthy of his Machiavellian TV namesake, Humphrey courted media attention and dodged political crises, not least of which was avoiding being mown down by Bill Clinton’s bulletproof Cadillac.

He also successfully fended off allegations of killing robin chicks and “savaging” a duck. John Major defended him, saying, “I am afraid Humphrey has been falsely accused.”

However there was a rift between Humphrey and Cherie Blair, who disliked cats and claimed to be allergic to them. It got to the point where spin-doctor Alastair Campbell had to engineer the world’s least convincing photo-op. Campbell had Humphrey sedated first.

Humphrey’s retirement in 1997 gave the Tories plenty of political ammo. “He could only take six months of Labour before he lost interest in living,” said Conservative spokesman Nigel Evans. There was even a rumour that Cherie had had him euthanised!

Humphrey was photographed with the newspapers of the day to reassure people he was still alive. Too old to catch mice, he retired with an annual government pension of £100 to the London suburbs, where he died in his sleep in 2006, aged 18.

The most recent mouser, Sybil, moved into Downing Street in 2007, but Humphrey proved a hard cat to follow. Her owner, Chancellor Alistair Darling, moved Sybil out after six months amid rumours that Gordon Brown disliked her. Sybil died in July 2009, and so the warrens of Downing Street await their next bureaucat.