American presidents have long had their own jet
The call for the new plane, which is already being dubbed "Blair Force One" and would especially be used in times of crisis, was made by Defence Secretary Geoff Hoon.
Mr Hoon told Parliament's influential Intelligence and Security Committee (ISC) it was important to have an aircraft fitted with secure communications equipment for Tony Blair to keep in close touch with their officials at all times.
But asked on Tuesday if there would be a prime ministerial plane, Tony Blair's official spokesman said: "No."
Britain's intelligence chiefs have backed the call for a special jet, saying that under present arrangements ministers can be out of touch for hours.
'Worth the money'
Ann Taylor, who chairs the ISC spy watchdog, has now given her support to the move.
In its annual report, which reveals Mr Hoon's appeal, the committee says: "We are persuaded that this expense can be justified."
Ministry of Defence sources said Ms Taylor's support was very helpful as in the past the government has been reluctant to order a purpose-built plane, which could cost up to £80 million and have presidential overtones.
There are now reports that the government is looking at converting a air-to-air refuelling jet for use by the prime minister and other ministers.
Such a conversion would cut down the costs considerably.
Custom built
Figures released by Downing Street last July put the overall cost of ministers' foreign trips at £5.6m over a year which included Mr Blair's post-11 September shuttle diplomacy.
Sources close to Mr Hoon say that chartering planes from British Airways for long haul trips, as happens how, costs more than the new plane.
Under the plans, the plane would have the latest security and communications equipment, as well as removable suites, including an office, bedroom, dressing room and kitchens.
It would also be able to tackle threats from surface-to-air missiles.
US presidents have had their own planes since 1944, when Franklin Roosevelt started using the "Sacred Cow".
The "Air Force One" call sign was first used in the 1950s for the presidential plane but it was President Kennedy's aircraft which first made the name popular.
The current "Air Force One" call sign is used by two specially configured Boeing 747-200B's used by President Bush.
UK Prime Minister Tony Blair is set to give the go-ahead for an order of two government jets. One jet is likely to contain 70 seats, whilst the other will be smaller with around 15 seats. Previously the Prime Minister has chartered aircraft or used a royal plane. Both planes would be second hand and not bought outright but leased on a long-term contract.

Government departments, as well as the royal family, who will have first priority, will be able to use the jets, but will have to pay for the full cost of travel. 

The story was first reported by BBC correspondent James Hardy, and comes out of a study into ministerial travel costs.

The nicknames 'Blair Force One' and 'Blair Force Two' have already begun to stick. American presidents have traditionally used a special jet called 'Air Force One'.