A contract to build the Royal Navy's two biggest-ever aircraft carriers was finally signed yesterday, securing the future of nearly 5000 jobs in Scotland and around 10,000 across the UK for up to a decade.

The 65,000-tonne ships, named HMS Queen Elizabeth and HMS Prince of Wales, will be built in modular sections then assembled at Rosyth in Fife, with launches planned for 2014 and 2016.

Defence Secretary Des Browne, who was in Govan, Glasgow, to attend the signing of the contracts, believed to be worth £4.2bn, said the vessels would play a vital role in enhancing the UK's defence capabilities.

Each 280-metre vessel is around the size and weight of the QE2 cruise liner, some 90 metres longer than the Invincible class carriers they will replace and will have a flight deck of 13,000 square metres - the equivalent of three football pitches.

When operational, they will carry a crew of 1450 and, eventually, 36 Joint Strike Fighters and four airborne early warning aircraft.

Their construction will create or secure 3000 jobs at Govan in Glasgow and 1600 at Rosyth. A further 1600 jobs are expected to be supported at two English yards, at Portsmouth and Barrow in Furness. When the knock-on effect of increased work for outside contractors is taken into account, the total number of jobs involved should reach 10,000.

Work on the ships' hulls will be carried out at Govan, Barrow and Portsmouth, while the bow sections and final assembly will take place at Rosyth.

The deal to construct the ships was reached after the formation of a joint venture, BVT Surface Fleet, formed by BAE Systems on the Clyde and VT Group in Portsmouth as the UK's sole warship builder.

It was greeted with jubilation by the Govan workforce yesterday, who, 10 years after the very future of the shipyards was put in serious doubt, were celebrating a level of job security not seen in a generation.

Joanne McGlinchey, a 21-year-old trainee mechanical engineer who started a three-year apprenticeship last August at the Govan yard, said: "It's been a great atmosphere. I think today has put everybody's mind at rest over their future on the Clyde."

She was joined yesterday by Steven Purcell, leader of Glasgow City Council, who paid tribute to the achievements of the workers. He said: "Today's announcement is incredibly important and historic. It's a great tribute to the skill, dedication and the hard work of those who, day in, day out, put in a shift on the Clyde.

"A decade ago, we were told that shipbuilding was dead and many Labour ministers shared that view. This workforce and this city made the case for continuing to build ships from the Clyde because they convinced the then government that we were as competitive as Poland and yards in the far east."

Greg Bain, 41, a plater who joined the BAE workforce at Govan two years ago, said: "I was born in Govan and my father was a shipwright. He died a while ago but I wish he could have seen that I was working here. Everybody thought shipbuilding was dying on the Clyde. I never thought I'd have the opportunity to come here."

The contracts, said by the Ministry of Defence to be worth £3.2bn but estimated at £4.2bn by insiders, will ensure work till around 2015.

Politicians who attended yesterday's ceremony expressed optimism the skills being developed among the Clyde workforce would ensure that future contracts could be won.