The F(x)tec Pro1 phone also has a bespoke shutter button on the side to click when taking photos.

The London start-up behind it said it wanted to "return the keyboard" to consumers.

Other handsets with keyboards built in, from brands such as BlackBerry Mobile and Swiss firm Punkt, were also on show.

"A lot of consumer tech still has buttons even though the tech is there to get rid of them," said Adrian Li Mow Ching, founder of F(x)tec.

"Haptic feedback never gives the same satisfaction as pressing a physical button.”

He said that the folding handsets unveiled by phone giants Huawei and Samsung demonstrated that "people want more than the single slab".

Zoe Kleinman with the Pro1

The handset I tried was a prototype, but it ran pretty smoothly. It was chunkier than a standard smartphone and a little heavier.

While I cannot deny that the sliding keyboard was fun to open, I did fear for the hinge and the plastic stand on which the screen sits at an angle.

The keys did take a little getting used to if you are more familiar with a touchscreen pad, but I found I made fewer typos when writing.

The Pro1 will go on sale in July for £649, or $649 in the United States.

F(x)tec says its apps have been optimised for landscape use

The Nokia 950 prototype inspired the Pro1

Lianchen Chen, who designed the device, describes himself as a BlackBerry fan. However, his device was inspired by a prototype from Nokia he was given in 2010, which was never released to the public.

The Nokia 950 had a slide-out keyboard hidden beneath the screen but was only ever given to app developers. Mr Chen said he used it until 2015.

The Pro1 features a full touchscreen in addition to its physical keyboard, an approach shared by BlackBerry Mobile's Key2.

Punkt’s MP02 phone is also covered in buttons, but it has limited functionality compared to modern smartphones. It is designed to be a so-called companion phone rather than a primary device.

Punkt's phone is a "companion" device

Punkt chief executive Petter Neby said the device would have been 75% cheaper to manufacture if it had just a touchscreen rather than physical keys. But he said physical keys gave people a more "optimal" experience.

“We press keys and buttons all the time and expect something to happen,” he told the BBC.

“The touchscreen is a convenience, it’s not optimal for a call to action.”

Both F(x)tec and Punkt deny that the hardware required for a physical keyboard limits the life of their devices.

Mr Neby says he still uses a 10-year-old BlackBerry with physical keys as his primary phone and has experienced no issues with it.

François Mahieu, global managing director for BlackBerry Mobile, told the BBC that people "value the productivity" offered with a physical keyboard experience.

"Many of our customers tell us there is a level of precision when typing on a keyboard that cannot be matched with a full touch experience," he said.

He said physical keyboards remained "relevant" and that BlackBerry devices "fill a distinct role in our device portfolio".

The BlackBerry Key2 sports a touchscreen and a keyboard

UK start-up Planet Computers is another company producing Android phones with physical keyboards. In 2018, it successfully crowd-funded a modernised "digital assistant" device, and is now working on a follow-up phone.

However, there is no indication that the broader mobile phone industry is planning a physical keyboard comeback.

“I am not sure if this is nostalgia or trying to find a way in the market serving those groups that the big guns have no interest in serving,” said analyst Carolina Milanesi from the consultancy Creative Strategies.

“I think this is really more what we see in a market where competing with the top players requires not just different hardware but a different approach to the market.”