A new strain of British genetically modified potato appears immune to the devastating fungus responsible for the great Irish famine of 1845, research has shown.

Late blight, caused by the organism Phytophthora infestans, remains the potato farmer's greatest enemy to this day.

The Irish potato famine of 1845 was a disaster for the poorer people of Ireland who depended on potatoes for food and income.

Over the following 10 years, more than 750,000 Irish men, women and children died and another two million left their homeland, with hundreds of thousands moving to the Glasgow area. Within five years of the famine, the Irish population was reduced by a quarter.

Glasgow city council has agreed to create a memorial in a city park to mark their arrival and plans are now under consideration.

Each year UK farmers spend around £60 million keeping the infection at bay with pesticides. In a bad year, losses and control measures combined can account for half the total cost of growing potatoes.

In the latest of a series of field trials, conducted in 2012, the fungus was unable to break down the defences of any of the GM potatoes.

Non-modified plants grown at the trial site were all infected after being denied protection from chemicals.

However, no-one can say at this stage how long the GM strain will hold out against blight, which is notorious for its ability to overcome resistance.

Scientists are now conducting further research aimed at identifying multiple resistance genes that will thwart future blight attacks.

"Breeding from wild relatives is laborious and slow and by the time a gene is successfully introduced into a cultivated variety, the late blight pathogen may already have evolved the ability to overcome it," said lead scientist Professor Jonathan Jones, from The Sainsbury Laboratory.

"With new insights into both the pathogen and its potato host, we can use GM technology to tip the evolutionary balance in favour of potatoes and against late blight."

Prof Huw Jones, head of the Cereal Transformation Lab, at the Rothamsted Research institute in Edinburgh, said: "Potato breeding is exquisitely difficult and moving disease-resistance from a wild relative to a commercial line by GM is a great way of overcoming these obstacles.

"Obviously a risk assessment is needed before these can be marketed but this is a great example of publicly-funded plant science with a real benefit to UK farming."

Because of late blight, potatoes are one of the crops most affected by chemical pesticides. In northern Europe, farmers typically spray a potato crop 10 to 15 times - even as many as 25 times in a bad year.

The new research, which focused on Desiree potatoes, addressed the problem of reinforcing blight resistance while maintaining crop characteristics pleasing to producers and consumers.

The aim was to produce a crop that could fight off blight without the aid of chemicals.

During three years of trials, the scientists grew potatoes containing a gene from a super-resistant wild strain from South America.

Normal cultivated potatoes naturally possess around 750 resistance genes, but in most varieties late blight is able to evade them.

The trials, managed by The Sainsbury Laboratory, took place at the John Innes Centre plant research institute in Norwich.

In 2012 the researchers took advantage of a year with ideal conditions for late blight. Instead of inoculating the plants, the scientists waited for them to be infected naturally by spores blowing on the wind.

By early August, 100% of the non-GM potatoes in the study were infected. In contrast, all the GM plants maintained full resistance against the pest until the end of the experiment.

The GM plants also produced a much greater potato yield. Tubers from each block of 16 GM plants weighed in at between six and 13 kilograms (13 - 28 pounds) compared with 1.6 - five kilograms (3.5 - 11 pounds) for non-GM plants.

Results from the trials, funded by the Biotechnology and Biological Sciences Research Council and The Gatsby Foundation, appear In the journal Philosophical Transactions of the Royal Society B.

The new hunt for multiple resistance genes is a joint project between the UK researchers and American company Simplot.

Prof Ian Crute, from the Agriculture and Horticulture Development Board, which promotes competitive farming, said: "It was here in Britain, over 170 years ago, that the science of plant pathology was born when this dreadful affliction of potatoes led to the discovery that severe crop loss could result from infectious disease.

"The fight against blight has been raging ever since. Now finally, we have the knowledge and technology to stack the odds in our favour. Surely, we must ensure that this scientific advance is exploited swiftly and not left on the shelf unexploited."