The company said it will purchase up to 50 two-storey trains for use across its entire network, which includes between London St Pancras and Paris, Brussels and Amsterdam via the Channel Tunnel.

It has reached a two billion euro (£1.7 billion) agreement for Alstom to build the trains in factories in France, where the manufacturer has its headquarters.

Eurostar has confirmed an initial order for 30 trains, and has an option for a further 20.

The fully electric fleet will be named Eurostar Celestia, which is derived from the Latin word caelestis, meaning “heavenly”.

Compared with the operator’s existing fleet of 17 single-decker Siemens-built e320s, the new trains will have 20% more seats, a lower floor and be 16cm taller.

Double-decker trains do not have twice as many seats as single-deckers because space is needed for interior steps.

The livery of the new trains has not been determined.

They will operate in addition to the e320s, meaning Eurostar will have up to 67 trains.

Eurostar has announced plans to add services from St Pancras to both Frankfurt and Geneva in the coming years.

It is scheduled to receiving Celestia trains in January 2031, with commercial services launching in the following May.

The trains will be the first major fleet of double-deckers on the UK’s railways.

A limited trial of two double-decker SR Class 4DD trains was conducted for services in London between Dartford and Charing Cross in the 1950s and 1960s, but they were withdrawn in 1971 because they were considered too cramped and expensive to maintain.

Double-decker trains are a common sight on the Continent, but the vast majority of the UK’s rail network is unable to accommodate them because of issues such as bridges not being high enough, and the distance between rails.

But the high-speed line between St Pancras and the Channel Tunnel was built to European standards, enabling it to be used by higher trains.

Eurostar chief executive Gwendoline Cazenave told the PA news agency the company awarded the contract to Alstom as it wanted to receive “bespoke trains as soon as possible”, ensuring it is “leading the race” to meet the growing demand for international train travel.

The “milestone order” is part of Eurostar’s “ambitious growth strategy” to reach 30 million passengers per year, up from 19.5 million in 2024, she said.

Ms Cazenave said passengers will enjoy a “special experience”, with enhancements such as more legroom and additional areas for bikes and wheelchair users.

She added that there will also be “surprise spaces”, which she did not provide further details about.

Passengers in all classes of travel will be able to choose between a seat on the upper deck or lower deck, with no price difference.

Alstom chief executive Henri Poupart-Lafarge said the announcement demonstrates Eurostar’s desire to “combine technological performance, energy efficiency and passenger comfort”.

He added: “This new-generation train, designed to meet the demands of international very high-speed traffic, embodies our vision of sustainable and competitive European mobility.”

Mark Smith, founder of international train travel website Seat61.com, said: “This is obviously good news for travellers.

“I have a soft spot for Alstom’s TGV Duplex used in France, and these trains are a new and improved generation.

“Book an upper deck seat for the best views.”

Eurostar plans to maintain the fleet – and its existing trains – at its Temple Mills depot in east London, which would be developed at a cost of about 80 million euros (£70 million).

The operator is expected to face competition in running passenger trains through the Channel Tunnel for the first time in its history.

Regulator the Office of Rail and Road is expected to announce a decision in the coming weeks on which company should be given access to the Temple Mills depot, which is critical to running services.

Companies developing plans to launch rival cross-Channel services include billionaire entrepreneur Sir Richard Branson’s Virgin Group, Italy’s state-owned railway company FS Italiane Group, and Gemini Trains, which is chaired by Labour peer Lord Berkeley.

Eurostar is majority-owned by French state railway company SNCF.

The UK sold its stake in the operator to private companies for £757 million in 2015.