Tony Blair has been accused of pouring water down the drain after figures showed Downing Street wastes thousands of gallons a year.
Figures released by the Government's green watchdog showed the Cabinet offices, including Downing Street, use 31.07 cubic metres of water, or 6,834 gallons, for each full-time employee a year, even though it is one of the smallest offices in Whitehall.
Their consumption in 2004-05 amounted to 9,300,000gal for 1,546 staff. It represents nearly twice the consumption of the next most thirsty Whitehall department and four times the Government's own target for Whitehall water use.
Yesterday the Cabinet Office insisted it had cut its consumption by more than three per cent during the last financial year. But officials admitted they still used 6,615gal of water per person in 2005-06.
Guidelines from Thames Water recommend that large offices with catering should use no more than 1,826gal per person each year if they are making efficient use of water.
The revelation comes amid a water crisis in London and the South East, with water companies calling on people to save water and the Environment Agency warning that consumers may have to use standpipes in the summer.
Environmentalists and MPs called on ministers to set an example at a time of huge pressure on supplies.
Peter Ainsworth, the Shadow environment secretary, said: "The performance of the Cabinet Office is atrocious. Just how clean do civil servants have to be? How clean does the Prime Minister have to be?
"The Government is constantly urging people to do better environmentally and to be more environmentally responsible but utterly failing to lead by example."
Chris Huhne, the Liberal Democrat environment spokesman, added: "This is clearly a case of do as I say, not as I do from the Government. They will be in no position to lecture anyone else on efficient use of water until they get their own house in order."
The Government set a target for departments to cut water use to 1,694gal per person per year by March 2004. But figures for 2004-05 produced by the Sustainable Development Commission show that only seven out of 22 Government departments hit the target. Five even reported an increase in water use last year. Figures for 2005-06 are due to be released this summer.
The commission warned that the Cabinet Office consumption was the "worst in Government" and called for a "step change" in progress. Its water consumption compared with 3,740gal for the next worst performer, the Treasury. No other department used more than 2,420gal of water a year per person. Last week, The Independent revealed that virtually no department was investing any funds in water recycling despite the targets for cutting water use and London facing its worst drought since 1976.
Alan Simpson, the Labour MP for Nottingham South and an environmental campaigner, said: "The Government seems to be saying 'shortage, what shortage?'. In New Zealand, Mr Blair said that he 'put the question of sustainability at the heart of what we try to do'. We just need to keep running that quotation back to him."
A Cabinet Office spokeswoman blamed the high consumption on its offices being in use 24 hours a day, but said officials were trying to cut down on waste by installing water-saving toilets, taps and showers.
She said: "There has been a steady downward trend in the amount of water consumed on a per person, per year basis since 2003-04 with a drop of almost nine per cent over the last two financial years. However the Cabinet Office recognises the need to improve further, is committed to seeking ways to reduce its water usage and is actively undertaking a number of measures to this effect."
Water consumption per person per year (2004-05)
* CABINET OFFICE 6,834 gallons (31.07 cubic metres)
* CONSTITUTIONAL AFFAIRS 1,474 gal (6.7m 3)
* CULTURE, MEDIA AND SPORT (not available)
* ENVIRONMENT FOOD AND RURAL AFFAIRS 1,494 gal (6.79m 3)
* EDUCATION AND SKILLS 2,241 gal (10.19m 3)
* INTERNATIONAL DEVELOPMENT 1,562 gal (7.1m 3)
* TRANSPORT 2,156 gal (9.8m 3)
* HEALTH 1,223 gal (5.56m 3)
* TRADE AND INDUSTRY: 1,793 gal (8.15m 3)
* WORK AND PENSIONS 2,244 gal (10.2m 3)
* FOREIGN OFFICE 1,716 gal (7.8m 3)
* HM CUSTOMS AND EXCISE 1,628 gal (7.4m 3)
* TREASURY 3,739 gal (17m 3)
* HOME OFFICE 2,376 gal (10.8m 3)
* INLAND REVENUE 1,606 gal (7.3m 3)
* MINISTRY OF DEFENCE (not available)
* OFFICE OF THE DEPUTY PRIME MINISTER 1,771 gal (8.05m 3)
* OFFICE OF NATIONAL STATISTICS
1,487 gal (6.76m 3)