THE offices of Australia's former prime ministers are costing more than $50,000 a week to run on top of an annual pension bill exceeding $1 million.

John Howard's office is the most expensive, with expenses averaging $850,000 a year over the last term of government, an investigation by The Sunday Telegraph has found.

Mr Howard's expenses blew out well in excess of the other four former prime ministers no longer in Parliament thanks to a $450,000 office refit in 2008/09 to his swanky digs in Sydney's MLC building, which already costs nearly $14,000 a month to rent.

There are six former PMs, but Foreign Minister Kevin Rudd who remains in Parliament and the Gillard ministry, does not yet qualify for the support that ex-leaders receive after they leave Parliament.The others are Gough Whitlam (1972-75), Malcolm Fraser (1975-83), Bob Hawke (1983-91), Paul Keating (1991-96) and Mr Howard (1996-2007).

Mr Keating's office is the most frugal as he keeps staffing costs low by engaging people on a part-time and ad hoc basis.

Each former PM is entitled to at least two staff, including a senior private secretary, and the annual wages bill of each is nearly $300,000.

Mr Keating saves about $70,000 a year by using staff as he needs them instead of full time appointees.

Mr Keating did not comment on the figures yesterday, nor did Mr Howard, whose office said he had dealt with these issues in the past when he refused to comment on revelations about his expenses bill after leaving office.

However, new figures have come to light revealing that in the seven months after leaving office, Mr Howard spent $109,892 on limousine services, evenly split between the government Comcar service and private hire cars.

Mr Howard's office rental was the highest at $13,853 a month, closely followed by former PM Malcolm Fraser, whose 101 Collins St office in Melbourne costs taxpayers $12,122 a month.

Former Labor PMs Whitlam and Hawke have offices on adjacent floors in Sydney's Potts Point at 100 William St. The monthly cost for each is $7464 and $7898 respectively.

Mr Keating's office is also in Potts Point, in Manning St, and costs slightly less at $7434 a month.

The former PMs also have their home and mobile phone bills paid by taxpayers, as well as unlimited allowances for publications, a private self-drive car, and air fares for them and their spouse.

These are in addition to their pensions under the generous former Parliamentary superannuation scheme, which gives them a pension indexed to current MPs' salaries for life.

The payout they receive depends on their length of service in Parliament, which is accelerated in the case of prime ministers and their final salary.

Each PM can usually expect to receive about 70 per cent of the incumbent's salary, unless they chose to take a lump sum on retirement.

Prime Minister Julia Gillard's current salary is $370,000, making the indicative pension for each former PM $250,000 a year.

Former Liberal PM Malcolm Fraser had the highest home phone bill at $281 a month, while Mr Howard had the highest mobile bill at $616 a month.

The figures were supplied by the Department of Finance using Freedom of Information laws and cover a 30-month period from December 1, 2007, to May 31, 2010.

Mr Howard, who last week released his tell-all book, Lazarus Rising, about his time in power has the highest Comcar bill averaging $2265 a month. The next highest was Mr Fraser at $818 a month.

The others averaged between $191 and $193 a month.

Mr Fraser, whose expenses have outstripped other former PMs in the past, has the most expensive private self-drive car at $1852 a month.

The cost of subscribing to newspapers and magazines also varies significantly.

Mr Whitlam and Mr Howard both spend more than $500 a month, while Mr Fraser spends $237 a month and Mr Hawke and Mr Keating are below $200.

Mr Fraser also has the highest postage bill at about $172 a month.

The Sunday Telegraph contacted Mr Fraser for a comment, but he was away from Melbourne and unable to respond, his office said.

The offices of Mr Whitlam and Mr Hawke also did not respond to our questions.