BAE Systems has been chosen as the preferred prime contractor in the £3 billion programme to build two new aircraft carriers for the Royal Navy – but the ships will be based on a design by former bidding rivals Thales UK, who are to be a major partner in the project.

Defence Secretary Geoff Hoon announced yesterday that the two defence contractors will form an alliance with the MOD to develop and build the ships, expected to displace up to 60,000 tons – making them the largest and most powerful surface vessels ever built in the UK, and three time the size of the present Invincible-class carriers.

They will act as mobile airfields for the world’s most advanced, stealthy supersonic jump-jet, the Lockheed Martin F35 – although the carriers will be capable of operating conventional jets with catapult launch systems if required during their lifespan. They will be able to handle almost 50 aircraft.

Mr Hoon said both bidders had performed “to a very high standard” for the right to lead “a massive and technically challenging programme”, which is expected to provide work for up to 10,000 people across the UK.

In weighing up the respective bids, Mr Hoon said: “Our detailed analysis shows that each company has significant strengths.

“BAE Systems has displayed a sound understanding of the complexities of the project, in terms of project management and prime contracting, and has developed a good relationship with all of the key shipyards.

“It has also demonstrated the skills necessary to integrate the different systems into an effective warship.

“Thales UK has provided an innovative design that is flexible enough to meet our needs. It has strengths in a number of key areas, including weapon and defence systems, and the interface between the ship, aircraft and flight deck operations.

“We have therefore decided that to deliver value for money and provide the best capability, it is important – and sensible – that we should exploit all of these strengths.

“We judge that a partnership appears to offer the best means of drawing in the resources and expertise necessary to deliver a programme of this magnitude.

“We envisage that this alliance will be led by BAE Systems as the preferred Prime Contractor, with responsibility for project and shipbuilding management.

“Thales UK will assume a major role as the Key Supplier of the whole ship design.

“We foresee that the Ministry of Defence will also take up a formal role within the Alliance for those parts of the programme for which we are rightly responsible. That would involve the management of appropriate risk and contingencies, and the provision of assets such as suitably-trained manpower and the Joint Strike Fighter aircraft.”

It is envisaged that the prime contract will be place in the spring of 2004, at which point shipbuilding can begin, and the carriers should enter service in 2012 and 2015.

The ships will be built at four yards – BAE Systems Marine at Govan, Vosper Thornycroft at Portsmouth, Swan Hunter on Tyneside and Babcock BES at Rosyth – although the involvement of other yards has not been ruled out.

The engines are likely to be built by Rolls-Royce.

First Sea Lord Admiral Sir Alan West said: “These ships and their aircraft will enhance the Royal Navy’s ability to be a powerful force for good in the world at great range from the UK and, most importantly, without host nation support.

“The joint air wing will be able to exert considerable influence on events over the land.

“It is important that these ships are brought into service on time in 2012 and 2015, and today’s announcement brings that a major step closer.”