There is no price tag yet for the ship, which will be crewed by the royal navy and is expected to be in service for about 30 years, although some estimates have put it as high as £200m.
And while construction is set to begin as early as 2022, the vessel, which could be named after Prince Philip, may not be ready for another three years.
The prime minister came under fire last year when it emerged he planned to repaint his official RAF plane red, white and blue, at an estimated cost of £900,000, prompting claims it would look like a “brightly coloured lollipop” in the sky.
Mr Johnson suggested the new ship would help the UK seize post-Brexit trading opportunities and reflect the UK’s “burgeoning status as a great, independent maritime trading nation”.
He added: “Every aspect… from its build to the businesses it showcases onboard will represent and promote the best of British – a clear and powerful symbol of our commitment to be an active player on the world stage.”
It is thought British businesses will be able to promote their products on the ship, which will sail all over the world, hosting trade shows and high-level negotiations alongside promoting British interests.
It will be the first national flagship since 1997 when the HMY Britannia was decommissioned.
The ship would play an important role in “achieving the UK’s foreign policy and security objectives”, No 10 said.
The government also wants to construct it in the UK, creating jobs and driving a “renaissance” in Britain’s shipbuilding industry.
The vessel will be built to reflect British design expertise and with a focus on the latest innovations in green technology, No 10 said.
But the ship could raise questions over how many modes of transport the prime minister needs to sell British interests abroad.
Defending the planned paint job on the prime minister’s plane last year, culture secretary Oliver Dowden said the government had always spent money “promoting the UK around the world” and that work on RAF Voyager was part of that effort.
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