British farmers have been presented with a solution to beat the shortage of fruit pickers post-Brexit - hiring a robot.

The machine, developed by Dogtooth Technologies, is said to be able to harvest to 200kg strawberries a day - and it doesn't need a visa or a toilet break.

Even before Brexit, farmers had been complaining that they were finding it increasingly hard to recruit labour to pick their summer harvests.

And last week a party of growers - including wine producers - attended a demonstration of robotic fruit picking organised by Produced In Kent to learn how the robots might help them in future.

Founder and CEO of Dogtooth Technologies, Dr Duncan Robertson, said: "Go back a few hundred years, before the Agricultural Revolution, and farming used to employ about one person for every hectare. "

"Now across the farming sector, the average is one person for every 100 hectares - except in horticulture, where it remains stubbornly at one per hectare, the same as in the 17th century."

"For us at Dogtooth, this is both a challenge and an opportunity."

"Everyone has seen the headlines about farms struggling to recruit enough labour, to recruit sufficiently skilled labour, and to retain the labour that they trained in previous years."

"Also the cost of employing labour has gone up because of the visa changes and the like."

"It is inevitable that in future robotic automation will help to address this problem in the same way that other forms of automation - the combine harvester for example - have done in the past."

"Our aim is to provide a complete substitute for human picking."

But Dr Robertson, who did his PhD in computer vision, insists this does not mean robots are doing people out of jobs.

He said: "Young people are just not willing to do the job any more."

"In Europe people can get better paid jobs in air-conditioned offices, sitting down all day. Farming is struggling to compete."

"We used to recruit fruit-pickers from Poland, then it was Romania, Bulgaria, Moldavia."

"Now we can't recruit fruit-pickers from Europe and have to go much farther afield - to Uzbekistan and Uganda."

"We aren't displacing jobs. We are replacing people who have already left the work-force!"

The robots work in teams moving autonomously along the crop rows, making a strange whirring noise as they grow.

Each robot has two picking arms and two "eyes" that allow it to see the colour of the fruit - and judge whether the berry is ripe for picking."

The robot picks the berry by the stalk, lowers into an onboard monitoring system that can instantly check whether it is free from disease or insect damage, and then places it straight into a punnet, sorted according to size.

Each team of about 10 robots has a human supervisor. If the robot has any malfunction it sends a message to the supervisor's computer tablet, and he or she can quickly respond.

The robot also automatically tells the supervisor when all the punnets are full and need replacing.

Dr Robertson explained that there were many reasons why robotic picking was attractive to growers - in addition to filling the labour gap.

Because the robots scan all the fruit as they pass along the rows - ripe and unripe - they can accurately predict future yields.

Farmers typically contract with supermarkets to supply fruit in seven to 14 days' time-but human estimating of crop yield can be out by up to 30 per cent, meaning farmers frequently end up with a surplus.

Dr Robertson said: "Better forecasting helps ensure more crop is sold at a higher profit margin."

Also because the robots pick by the stalk, there is less bruising of the fruit and a reduced risk of disease transference, meaning the fruit ends up with a longer shelf life.

And because the robots can fill the punnets accurately to the supermarkets' weight specifications, there is reduced over-filling - which is wastage from the farmer's point of view, although shoppers might be happy to get a bit extra.

Dr Robertson said: "We can essentially package in situ."

"If a berry is rotten, the robot will pick it because we don't want to leave that berry in the field as a home for insects to lay eggs - but then it is set aside."

"If one berry with mildew gets into a punnet, it quickly affects the others, we don't want that."

"The established practice at present is for that work to be done in a packhouse where a line of people stand weeding out defective berries, but the fruit leaving our robots is immediately ready for retail, eliminating the need to operate an inspection line in the packhouse, and this also minimises the handling of the fruit."

Dogtooth, based near Cambridge, currently has a fleet of about 70 robots that pick "many tens of tons of fruit each season" both in the UK and in Australia."

Each year, the company has produced a new generation of robots, improving each time.

This year, it is launching its fifth generation, which it will sell directly to its customers as a capital investment.

It expects to manufacture another 50 robots in the next six months.

The robots are battery-powered and previously had to be recharged overnight, while the 5th generation have removable batteries, which means the robots can be kept working 24 hours a day.

Dr Robertson said: "The extraction rate is the name we give to the proportion of ripe berries that the robots can pick."

"For a human, the extraction rate might be 95 per cent. For our 4th generation of robots, it was typically 60 to 70 per cent, but for our 5th generation, it's typically 80 to 90 per cent, so we are increasingly close to human pickers."

At present, any missed fruit still has to be picked by hand - in what is termed a "clean-up" operation."

Dr Robertson said that a high extraction rate was essential, otherwise the cost of the clean-up began to make the process unprofitable.

He added: "But, the other measure of quality is wastage. So for every 100kg of fruit we pick, how much do we waste by causing damage to the crop?"

"For human pickers, the proportion is around 2.5 per cent, for robots it is actually less."

"And another thing that we have noticed about our picking here in Kent is that our robotic husbandry reduces mildew at the end of the season."

Dr Robertson believes robotic picking will be attractive to farmers because it will give them greater control.

He said: "Recruiting labour is a massive administrative problem for them."

"The best pickers are brilliant, but 20 per cent of the workforce last for a week and then quit."

"Then there is all the headache that goes into providing them with accommodation, visas transport."

One wine-grower on the tour agreed. He said: "It would be worth it just not to have to keep shifting the mobile toilets around!"

At present, the robots only pick strawberries.

Dr Robertson said: "We started with strawberries for a very good reason."

"The harvest season is a lot longer. Most of our customers are producing strawberries in glass houses or poly-tunnels for about nine months of the year."

"That's great in terms of the capital utilisation of our robots."

"We may struggle to be commercial for crops like grapes - at least initially - because the harvest window is so short."

"If you can only operate the robots for three weeks a year, then for the other 49 weeks they are sitting in the shed doing nothing."

However, the company is working on prototype robots to pick raspberries, apples and tomatoes.

Dr Robertson said: "The standing joke in the industry is that robotic harvesting has been just three or four years away for the last 20 years."

"But our Gen 5 robot can typically pick 200kg of fruit a day - which is comparable to what a human might achieve."

"It has been a long journey. It has taken us five generations to get something that we can sell as commercially relevant."

"But now we're actually there."