When did grey squirrels start posing a threat to reds in the UK?

Paskett, though, thinks there could be an effective additional way to control grey squirrel numbers within the next five years.

He said the Red Squirrel Survival Trust was jointly funding a field trial by the government’s Animal and Plant Health Agency.

Beginning “later this year or early next year” Paskett said his organisation had “developed the means to deliver oral contraceptives to grey squirrels using a ‘hopper’ which sees the squirrel lift up a lid” to access them.

Because greys typically weigh 500g – approximately twice that of reds, only they can access the contraceptive.

If the field trial is successful, Paskett hopes landowners and forest rangers will be able to sign up to the scheme.

For now, though, Foott said shooting and trapping were the main options.

However, she said: “The reintroduction of pine martens can help. Because they are a native species in the UK, they evolved together with red squirrels.

“They do eat red squirrels but the reds know to quickly get out of their way and will send out the alarm signal to the rest of the colony.

“The greys are a little bit stupid and will say ‘hello, I haven’t seen you before’ and the pine marten will get them!”