The two new carriers would be the biggest in Royal Navy history
The Royal Navy's two new aircraft carriers are likely to enter service a year or two later than planned, Defence Secretary John Hutton has announced.
In a statement to MPs, he added there would be no delay in construction - but work would continue at a slower pace, sustaining jobs for longer.
The £4bn shipbuilding project is due to begin next spring.
The announcement affects shipyards in Appledore, in north Devon, Portsmouth, Barrow-in-Furness, Glasgow and Rosyth.
Mr Hutton said: "We have concluded that there is scope for bringing more closely into line the introduction of the Joint Combat Aircraft and the aircraft carrier. This is likely to mean delaying the in-service date of the new carriers by one to two years.
"We are in close consultation with the Aircraft Carrier Alliance on how this might best be done. Construction is already under way and will continue.
"The programme will still provide stability for the core shipyard workforce, including 10,000 UK jobs."
Glasgow South West MP Ian Davidson said that spinning out the order would mean continuing work for the shipyards.
Mr Davidson said: "The good news is that the biggest naval order since the Second World War will remain in place.
"The better news in my view is that the order is going to be spun out, which means that the yards will be in work longer."
But Scottish National Party MSP Nicola Sturgeon, whose Govan constituency includes some of the shipyards due to build the aircraft carriers, called on the government to pledge there would be no job losses.
She said: "These contracts were supposed to be signed, sealed and ready to be delivered.
"I will be in contact with John Hutton to secure a guarantee that there will be no delay in starting these contracts and that no gap will be allowed to appear in the contracts for Govan, Scotstoun or Rosyth."
Plymouth MP Linda Gilroy said shipyard workers in north Devon should be put at ease by the announcement over the carriers' future.
She said: "This is a question of slowdown, of perhaps delaying the second carrier and slowing down the first one.
"I don't think Appledore need worry too much about its part in that."
Des Browne gave the green light for the construction of HMS Queen Elizabeth and HMS Prince of Wales in May, when he was defence secretary. Contracts worth about £3.2bn were signed in July.
BBC defence correspondent Caroline Wyatt said the government did not view cancelling major defence projects as an option, but considered delays as a way of controlling the Ministry of Defence's (MoD) spiralling budget.
Liberal Democrat MP Mike Hancock, a member of the Commons Defence Committee, said the MoD was in financial "chaos".
Meanwhile, hundreds of jobs in Somerset are to be secured due to a new government order for 62 Future Lynx helicopters from Agusta Westland, BBC West has learned.
An immediate contract will also be awarded to upgrade existing Lynx helicopters to prepare them for battlefield sites such as Afghanistan.
The order, worth £1bn, has been delayed for more than two years.