Deep cuts to the defence budget will see the Royal Navy's flagship aircraft carrier and its fleet of Harrier jets scrapped "with immediate effect", according to Government sources.
The move is among wide-ranging measures to be unveiled by Prime Minister David Cameron as part of the military's share of the Coalition's severe public spending squeeze.
He is also expected to confirm that the Strategic Defence and Security Review (SDSR) has concluded that the renewal of the Trident nuclear deterrent will be delayed.
The immediate axing of HMS Ark Royal will leave the UK without an aircraft carrier capable of flying jets for around a decade while two new vessels are built at a cost of £5.2 billion.
That project was spared the axe after it was found abandoning the contract - with one of the two already under construction - would end up costing the taxpayer more.
Although the first is set to come into service in 2016, converting it to allow it to be used by jets from allied nations could take several years.
Defence Secretary Liam Fox has insisted the long gap in Britain's aircraft carrier capability will not affect its defence abilities - despite warnings from former Navy chiefs.
But Mr Cameron was reported to have told the Cabinet it was one of the hardest decisions he had faced since becoming Prime Minister.
Under the SDSR, all three services face manpower cuts, the Army is expected to lose large numbers of tanks and the RAF to see bases closed and fighter jets axed.
