Ministerial car use has increased by nearly a fifth, provoking criticism of the government's green credentials.
Figures obtained by the Liberal Democrats show the Government Car and Despatch Agency ferried ministers nearly three million miles last year, equivalent to driving around the world almost 115 times.
The service employs nearly 200 chauffeurs to drive government ministers.
Lib Dem transport spokesman Alistair Carmichael attached the environmental and monetary costs of ministerial travel, calling on the government to justify the increase in car use.
It is estimated that the agency will cost tax payers nearly £18 million this year, while official travel emits "hundreds of tonnes" of carbon dioxide.
"It is time to bring these spiralling costs under control. The government must justify this massive increase in ministerial car use," argued Mr Carmichael.
He added: "Climate change is the biggest threat our planet faces. It is vital that everyone does as much as possible to cut down on carbon emissions.
"Transport currently accounts for over a quarter of the UK's CO2. Government ministers need to start leading by example."
The environment secretary David Miliband will today attend a question and answer session at a screening of An Inconvenient Truth, Al Gore's Oscar winning documentary on global warming.