Image copyright Ministry of Defence Image caption This computer-generated image shows how the ships will look

The Queen will officially name the Royal Navy's new aircraft carrier HMS Queen Elizabeth at a ceremony on 4 July, the Ministry of Defence has said.

The event will be held at Rosyth dockyard in Fife where work to assemble the vessel is being completed.

Defence ministry officials say the 65,000-tonne ship is "the most complex warship ever built in the UK".

The estimated cost of the aircraft carrier and its sister ship is £6.2bn. The initial projected cost was £3.65bn.

Building HMS Queen Elizabeth and the second carrier, the Prince of Wales, has been one of the biggest defence projects ever undertaken in the UK.

It has been beset by construction and design delays however.

During the course of the project, an order for carrier jump jets - capable of short take-offs and vertical landings - was switched to jets with a longer range that could carry more weapons.

But the MoD later decided to revert to the original jets for logistical and financial reasons.

Labour's Margaret Hodge, the chairwoman of the Commons Public Accounts Committee, said last year that the "U-turn" involved £74m of taxpayers' money going "down the drain".

Image copyright Ministry of Defence Image caption The aircraft carrier has been built in shipyards in Clyde, Rosyth, Portsmouth, Birkenhead, Tyne and Devon

Image copyright Ministry of Defence Image caption The 65,000-tonne ship will become Britain's biggest-ever carrier

The ship will be named in a traditional champagne ceremony.

Members of HMS Queen Elizabeth's crew, and workers who have helped to build the ship, will be among thousands of people expected to attend.

The construction of the aircraft carrier has sustained about 7,000 jobs at more than 100 companies across the country, the MoD said, describing it as "Britain's biggest-ever carrier".

Defence Secretary Philip Hammond said: "This will be a proud and historic day, not just for the Royal Navy but for the entire nation.

"It is great news that Her Majesty will officially name the first aircraft carrier HMS Queen Elizabeth."

War fighting credibility

He added: "This occasion will mark a major milestone in regenerating the UK's aircraft carrier fleet and its power projection capability."

Later in July, the dock at Rosyth will be flooded to allow HMS Queen Elizabeth to float for the first time. Sea trials will then begin in 2017 with flight trials of Lightning II aircraft starting the following year.

Admiral Sir George Zambellas, First Sea Lord, said the ship would be the "first of a class that will return fast jet carrier operations to our nation's war-fighting credibility".

He said: "We have a great journey ahead, in close partnership with the Royal Air Force, to create and sustain the best that our shipbuilding, engineering, technology and people can deliver.

"And we are proud to have the chance to show what we can do."

Contracts 'renegotiated'

Work is already under way on HMS Queen Elizabeth's sister ship, the Prince of Wales, which will start to be assembled in Rosyth dockyard later this year.

The MoD said the defence secretary last year renegotiated contracts to ensure the costs of the "biggest ever ships in the history of the Royal Navy" did not spiral.

"The defence secretary announced a successful renegotiation of contracts between the MoD and industry last year, to prevent further cost increases and save the taxpayer hundreds of millions of pounds," a spokesperson said.

"This ensures any further cost increase is shared equally with industry and provides an incentive to manage this vast project efficiently and effectively."