A major U-turn over the fighter aircraft for the Royal Navy's new carriers is expected to be confirmed on Thursday.
Ministers are expected to say they have now opted for the jump-jet variant of the US-built F-35 Joint Strike Fighter - as planned by the former Labour government.
The decision - which had been expected before Easter - is believed to have been finally signed off by David Cameron at Tuesday's meeting of the National Security Council.
Under the 2010 Strategic Defence and Security Review, the coalition had planned to switch to the carrier variant - the F-35C - arguing it was a more capable aircraft and, unlike the F-35B jump jet, would be inter-operable with the US and French navies.
However the costs of fitting the necessary catapults and arrester gear to one of the carriers reported to have spiralled from an estimated £400 million to almost £2 billion.
Nevertheless the decision will be an embarrassment for the Prime Minister who strongly criticised the original decision by Labour to choose the jump jet.
Shadow defence secretary Jim Murphy said the Government's "chaotic" handling of its carrier policy totally undermined its credibility on defence.
"This is a personal humiliation for David Cameron who will to return to Labour's policy, which he previously condemned," he said.
"This is a strategically vital element of the equipment programme on which our security and thousands of jobs depend and yet ministers have treated it with hubristic incompetence, wasting hundreds of millions at a time of painful defence cuts."
On-duty police officers applaud as thousands of off-duty police officers march pass Downing Street in London as they take part in a protest march against proposed changes to their pay and conditions, in London, Thursday, May 10, 2012. Up to 16,000 police officers, who are banned from striking under law, donned black caps representing each officer expected to be lost under the Government's budget cuts as they took to the streets of London Thursday. (Photo credit: AP Photo/Sang Tan)
A protester holds up a placard in front of Downing Street in London as thousands of off-duty police officers march past in a protest against cuts in the police service, Thursday, May 10, 2012. (Photo credit: AP Photo/Sang Tan)
Police officers and public sector workers march through central London during a day of protest across the country on May 10, 2012 in London, England. A reported 400,000 public sector workers across the country are taking part in a twenty four hour strike in dispute over government changes to pensions. (Photo credit: Dan Kitwood/Getty Images)
Andy Coulson, former editor of the News of The World and former director of communications for the Conservative Party, arrives at The Royal Courts of Justice to give evidence to the Leveson Inquiry on May 10, 2012 in London, England. This phase of the inquiry into the culture, practice and ethics of the press in the United Kingdom is looking at the owners of various media groups. The inquiry, which may take a year or more to complete, comes in the wake of the phone hacking scandal that saw the closure of The News of The World newspaper in 2011. (Photo credit: Christopher Furlong/Getty Images)
Syrians inspect a crate at the site of twin blasts in Damascus on May 10, 2012. Two powerful blasts in quick succession rocked the Syrian capital at morning rush hour, killing and wounding dozens of people, state television said, blaming the attacks on 'terrorists.' (Photo credit: LOUAI BESHARA/AFP/GettyImages)
Syrians inspect damages at the site of twin blasts in Damascus on May 10, 2012. Two powerful blasts in quick succession rocked the Syrian capital at morning rush hour, killing and wounding dozens of people, state television said, blaming the attacks on 'terrorists.' (Photo credit: LOUAI BESHARA/AFP/GettyImages)
A high priestess, holds a torch with the Olympic flame during the lighting of the flame ceremony on Thursday, May 10, 2012, in Ancient Olympia, Greece. The flame will be carried from the birthplace of the Ancient Olympics to London, where the 2012 Summer Games will take place from July 27-Aug. 12. (Photo credit: AP Photo/Petros Giannakouri
A relative weeps as she waits for the news on the missing Russian airplane at Halim Perdanakusuma airport in Jakarta, Indonesia, Thursday, May 10, 2012. The wreckage of the Sukhoi Superjet-100 passenger plane that went missing during a demonstration flight Wednesday near Jakarta was spotted Thursday in a mountainous area of West Java. (Photo credit: AP Photo/Tatan Syuflana)
An Elderly woman participates in a protest in New Delhi, India, Thursday, May 10, 2012. Hundreds of elderly from the country are protesting near the Indian parliament for the last three days demanding universal old age pension for those above 60 years of age. (Photo credit: AP Photo/ Manish Swarup)
Protestors shout slogans during a general strike to pressure lawmakers drafting the Himalayan nation's new constitution not to divide the country into states based on ethnic population which could fuel racial conflicts later, in Katmandu, Nepal, Thursday, May 10, 2012. Police says they have detained more than 50 protesters who were enforcing a general strike called to pressure lawmakers drafting the Himalayan nation's constitution. (Photo credit: AP Photo/Niranjan Shrestha)
Kashmiri government employees shout slogans as Indian police use colored water from a water cannon to disperse them in Srinagar, India, Wednesday, May 9, 2012. The employees demanded payment of arrears in salaries and raising of retirement age, among other demands. (Photo credit: AP Photo/Mukhtar Khan)
Fancy rat Vaice wears fan gear of German Bundesliga soccer club Borussia Dortmund during a photo call for the trade fair Dog & Pet (Hund & Heimtier) in Dortmund, Germany, 09 May 2012. More than 8500 dogs from 35 countries representing 267 breeds are expected at Westfalenhalle for the VDH European Champion Exhibition from 11 till 13 May 2012. Cats, fish, reptiles and rats, et al will also be on view. (Photo credit: BERND THISSEN)
Wounded Syrian soldiers react following a roadside bomb attack which targeted their convoy as they escorted UN peace observers, including the Norwegian general who heads the mission, in the restive southern Syrian city of Daraa on May 9, 2012. Six soldiers were wounded when the explosive device, which appeared to have been planted underground, detonated as the convoy of four vehicles was about to enter Daraa, cradle of a 14-month uprising against President Bashar al-Assad's regime. (Photo credit: LOUAI BESHARA/AFP/GettyImages)
Tulips to pick yourself shine in various red tones near Schondorf, Germany, 09 May 2012. (Photo credit: KARL-JOSEFÂ HILDENBRAND)
Dancer TsaiÂ Ming-yuan and Ko Wan-chen dance during a press rehearsal for the European premiere of the piece Water on the Wall by the Cloud Gate Dance Theater of Taiwan in Wolfsburg, Germany, 09 May 2012. The Moviementos dance festival runs until 20 May with dance, readings and concerts. (Photo credit: JOCHENÂ LUEBKE)
A Kenyan Tribesman performs in the rain during the dress rehearsal of the Diamond Jubilee Pageant which runs from Thursday 10th May to Sunday May 13th in the grounds of Windsor Castle, Berks. (Photo credit: Steve Parsons/PA Wire)
The Carousel of the Carabinieri perform in the rain during the dress rehearsal of the Diamond Jubilee Pageant which runs from Thursday 10th May to Sunday May 13th in the grounds of Windsor Castle, Berks. (Photo credit: Steve Parsons/PA Wire)