Thousands of Scottish shipbuilding jobs are under threat after the boss of BAE Systems admitted a £5.2billion defence contract could be cancelled.

Chief executive Ian King said the Ministry of Defence had asked him to look at different options over the building of two super-carrier warships at Govan and Scotstoun on the Clyde, and Rosyth on the Forth.

And unions today demanded an urgent Government statement on the situation as crisis talks were planned.

Mr King told the House of Commons Defence Committee: “The programme is for two vessels but the options range from one vessel to no vessels, but having an equivalent programme to maintain skills.”

Union officials, along with conveners at both yards, were expected to meet local management today.

Jim Moohan, chairman of the Confederation of Shipbuilding and Engineering Unions, today hit out: “The continuing speculation is very worrying at a time when the Government won’t be announcing its cuts until late October. We are being kept in limbo until then.

“It would be in everyone’s interested if the Government made a statement now. This speculation is damaging to the company, to the workforce, to contractors and to suppliers.”

Mr Moohan said he was hoping to be given information at today’s meeting which would help “calm fears” among workers.

Mr King made clear to the Defence Committee that if the project was cancelled then it would effectively sound the death knell for shipbuilding on the Clyde and Forth: “If you terminate these carrier programmes, you lose a capability that you cannot replace.”

Jim Murphy, the Shadow Scottish Secretary, said: “For all their denials, it is now exposed that the Tories are actively looking at cancelling the whole project.”

Mr Moohan pointed out that the Clyde yards at Scotstoun and Govan have a 15 year commitment of work from the Government and despite the latest revelations he remains confident that both yards will survive even if the carrier programme was scrapped. He won’t, however, predict how many jobs could be axed. While 4000 shipbuilding jobs would be lost by any cancellation of the contract, it is thought that as many as 10,000 direct and indirect posts could be affected.

Work on HMS Queen Elizabeth is well under way and work has also begun on HMS Prince of Wales. They are due to enter service in 2014 and 2016 respectively.

Orders for key equipment worth more than £1bn, together with 80,000 tonnes of steel, have already been placed.

The 280yard-long carriers – which, at 65,000 tonnes, will be the largest warships ever built in the UK – will each be capable of carrying up to 40 aircraft.

The ships are being constructed in sections at locations around Britain and will be shipped to Rosyth to be fitted together.

Ian Davidson, the Labour MP for Glasgow South West said: “I’m confident once the assessment has been made, including the costs associated with closure, ministers will recognise that it makes financial sense to continue.”

Stuart Patrick, chief executive of Glasgow Chamber of Commerce, said: “These shipyards are vital to the city’s economic prosperity and it is important that they continue their prominence and success.”

An MoD spokesman said: “The Defence Secretary (Dr Liam Fox) has made clear that tough decisions will need to be made, but the complex process of a strategic defence and security review will be concluded in the autumn and speculation now is entirely unfounded.”

Over several months, the issue of the carriers has become a battleground, with Labour accusing the Tories of not giving guarantees on the contract’s future and the Government insisting everything, other than the renewal of Trident, has to be part of the defence review.

The Government has always maintained that, where cuts of between 25% and 40% are being considered, every single option has to be examined.

Nonetheless, suggestions last week that Britain was considering sharing carriers with the French were denied by Dr Fox, who said such a proposal was unrealistic.