The Foreign Office today defended seeking to hire a private jet for the use of Foreign Secretary David Miliband.
A contract for the hire of a charter aircraft went out in February and will last for two years, it is understood.
A department spokesman said recent changes in ministerial flight availability meant officials sometimes needed to charter aircraft at short notice, adding: "Value for money is a top priority."
He said: "Unlike a lot of other countries we don't have a Foreign Office plane.
"We always try to use commercial airlines but sometimes that is not practical. Until now we have been able to use the RAF in those circumstances.
"Changes in the RAF mean we need the ability to charter aircraft sometimes at short notice - value for money is a top priority."
The contract for the aircraft hire has not yet been issued.
According to the News of the World, the tender document says officials are looking for "a good quality aircraft for overseas visits by the Foreign Secretary".
The company must "provide a first class service" and be able to "provide an aircraft sometimes within a few hours' notice", it added.
Mr Miliband, who last week flew to Sri Lanka for an official visit, made more than 20 state trips last year to countries including Turkey, Syria and the United States.
Matthew Elliott, chief executive of the Taxpayers' Alliance, told the News of the World: "David Miliband would do a better job if he remembered he is there to serve the people, not live a life of luxury at our expense."