Details of the upgrade will be at the centre of the Government’s Strategic Defence and Security Review (SDSR), due to be set out to the Commons by Prime Minister David Cameron today.
Mr Osborne said the move would put the UK second only to the US in carrier capability and mean it could respond to threats “wherever and whenever necessary”.
The government had proposed to have only eight of the US-built F35 Joint Strike Fighter aircraft available for deployment to the new carriers HMS Queen Elizabeth and HMS Prince of Wales by 2023.
That has now been trebled to 24 – all in strike roles if required – with the 18 others on order being used in the training fleet or in maintenance, the Chancellor said.
Capability could be temporarily “surged” to 39 jets to respond to specific threats.
Defence spending received a boost in the Budget, when the Chancellor declared that the UK would continue to meet a Nato target to devote at least 2 per cent of national wealth to defence.
It has already been announced that the SAS and other special forces will get an extra £2 billion to improve their equipment, the RAF will double its number of drones, an extra £1.9bn will be spent on cyber security and 1,900 new spies recruited.
The SDSR is also expected to reveal that the expected cost of renewing the UK’s nuclear deterrent has risen – with the SNP warning against cutting the number of anti-submarine frigates to be built in Scotland to compensate.
Enhancing the carrier capability to ensure at least one is available would enable the UK to contribute to international missions such as the one against Islamic State (IS) from the Gulf, source said.
It has also been claimed that it would mean the UK was able to respond to any future attempt by Argentina to invade the Falkland Islands, something critics have claimed Britain can no longer do.
Mr Osborne said the policy was also worth £29bn to the UK businesses in the supply chain, including BAE, Rolls-Royce and ejector seat manufacturer Martin Baker.
He said: “My spending review this week is all about security – national and economic.