When did grey squirrels start posing a threat to reds?

Endangered red squirrel populations have plummeted from about 3.5 million to less than 300,000 in the UK, with their grey-haired rivals continuing to thrive.

But when exactly did the squirrel stand-off begin and how bad has the situation become?

The Woodland Trust reckons there are only 39,000 of them left, while the Save Our Reds campaign thinks just 15,000 remain, including in conservation areas such as Formby on Merseyside.

In May the group warned that red squirrels, which "still cling on" in parts of northern England, could disappear entirely within 25 years.

In stark contrast, since their introduction from North America in the 19th Century, greys have thrived at the expense of their distant cousins, which compete for habitats and carry lethal viruses.

The first verifiable importation of greys , external is widely understood to have come 150 years ago, when a Victorian banker named Thomas V. Brocklehurst is said to have released a pair of greys into Henbury Park, near Macclesfield in Cheshire, that he had brought back from a business trip to the United States.

The rest, they say, is history and nobody back then would have realised the unintended lasting consequences of his actions.

According to Graham Paskett from the Red Squirrel Survival Trust, there are now between 2.5 million and 2.7 million greys in the UK.

Jackie Foott, from the British Red Squirrel conservation group, told the BBC that reds and greys cannot coexist in the same location and that to protect the reds you have to "get rid of the greys - we realised that a while ago".

She explained: "The grey squirrel is a pest, non-native, invasive species.

"People don't realise just how much damage they are doing to trees, crops and properties - they cause at least £40m damage to forests and forestry services each year."

"Greys outcompete reds for habitat and food - they don't actually physically attack them but they do bother them," said Foott.

"Secondly, greys have squirrel pox - it doesn't affect them but they transmit it to red squirrels and it's fatal for them. It's a horrible disease and causes them ulcers and blindness."

"Fertility control isn't available now - and has the effect of affecting other species, including reds," said Foott. "Gene therapy is probably at least 10 years away.