It has long been thought grey squirrels were hardy invaders and were able to interbreed into a 'supersquirrel' species that adapted and spread around the UK, conquering vast areas.

But new DNA analysis of squirrels living more than 500 miles (804km) apart has proved there is no super species, and greys are ultimately 'genetically distinct'.

This suggests that humans are to blame for introducing the species to places such as Scotland, where their presence ultimately put the survival of native reds north of the border at risk.

It has long been thought grey squirrels were hardy invaders and were able to interbreed into a 'supersquirrel' species that adapted and spread around the UK. But DNA analysis of squirrels living more than 500 miles (804km) apart has proved there is no super species and greys are ultimately 'genetically distinct'

The species originated from North America but arrived in the UK in the 1890s - and out-competed native red squirrels for resources and carried diseases which killed their vast population off.

During her PhD studies at Imperial College London, Dr Lisa Signorile compiled a DNA database of nearly 1,500 grey squirrels in the UK and Italy and traced where populations of grey squirrels have come from.

SQUIRRELS OVER INDULGE IN THE WARM WINTER WEATHER The unusually mild winter temperatures in many areas this year has caused flowers to bloom early, trees to blossom and even produced some of the earliest crops of asparagus ever seen. But the abundance of food and warm weather also seems to have been having an effect on squirrels too – by making them fat. Sightings of seemingly overweight squirrels have swept social media sites as the rodents take advantage of the mild conditions to cram in extra food in preparation for the cold weather, when it finally arrives. In Cardiff’s Bute Park in Wales, grey squirrels puffed up with extra food and thick fur have been spotted scampering around, albeit a little slower than normal. Although grey squirrels do not hibernate - they are active all year round - they usually pile on extra weight to help them survive the lean cold months of winter, when they must rely upon food they have stored. Advertisement

She found that a population of grey squirrels in Aberdeen was most closely related to grey squirrels some 560 miles (901km) away in Hampshire's New Forest, and not nearby groups.

Another, individual grey squirrel captured on the Isle of Skye in 2010 had actually come from Glasgow, more than 200 miles (321km) away.

In this case, its genetic profiling confirmed a report the squirrel had stowed away under a car bonnet and escaped on Skye, and now researchers have ruled the only way greys have spread around the UK is by similar means - being transported by humans.

'It has been thought since the 1930s that grey squirrels were all the same, spreading across the country as one invasion front,' explained Dr Signorile.

'After a century, genetics has proved that this isn't correct.

'They are not that good at breeding and mixing - in fact there are clear signs of inbreeding.

'Grey squirrels are not such crazy invaders as we think - their spread is far more our own fault.'

During her studies, Dr Signorile also discovered one of the worst offenders at spreading grey squirrels was the 11th Duke of Bedford Herbrand Russell, who died in 1940.

This, instead, suggests humans are to blame for introducing the species to places such as Scotland, where their presence ultimately put the survival of native reds (stock image) north of the border at risk. During her PhD, Dr Lisa Signorile compiled a DNA database of nearly 1,500 grey squirrels in the UK and Italy

The species originated from North America but arrived in the UK in the 1890s. They out-competed native red squirrels for resources and carried diseases which killed their vast population off. Grey squirrels (pictured) have largely displaced red squirrels in England and Wales, and less than 120,000 remain in Scotland

Dr Signorile also discovered one of the worst offenders at spreading grey squirrels was the 11th Duke of Bedford Herbrand Russell (illustrated)

He was involved in many successful animal conservation projects, but released and gifted many grey squirrels around the UK from his home at Woburn Park, Bedforshire.

He also released populations in Regent's Park, likely creating the London epidemic of greys.

Dr Signorile said: 'It was a time when we didn't know invasive species could cause so much damage.'

Grey squirrels have largely displaced red squirrels in England and Wales, and less than 120,000 remain in Scotland - 75 per cent of their total UK population.

They still outcompete native reds and carry diseases that kill them, and Dr Signorile called on conservation programs to continue to try and save them while humans unwittingly help greys spread.

She said: 'Eradication or control programs are still needed, in particular in areas where red squirrels are present.

'We put a lot of money into controlling grey squirrel numbers, but nobody is trying to prevent their movement and discourage people from picking them up.

'Decision-makers should look into preventing spreading of greys by human hands.

'The public also needs to be aware of the risk of even accidentally moving squirrels.

'People think grey squirrels are already everywhere, so it is not a problem, but it can be, especially in areas of Scotland where there are not yet established populations.'