Sir David Attenborough, who is launching the Study of Nature report, called it a "stark warning" but also "a sign of hope".
Sir David said: "For 60 years I have travelled the world exploring the wonders of nature and sharing that wonder with the public. But as a boy my first inspiration came from discovering the UK's own wildlife.
"Our islands have a rich diversity of habitats which support some truly amazing plants and animals.
"We should all be proud of the beauty we find on our own doorstep; from bluebells carpeting woodland floors and delicately patterned fritillary butterflies, to the graceful basking shark and the majestic golden eagle soaring over the Scottish mountains.
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A humid night for some with thundery downpours in places.
The 20-year-old was found fatally wounded on Roth Walk, near Finsbury Park, north London at around 3am on Saturday, Scotland Yard said.
Daniel Cowell has been jailed for five years and four months after ramming a police patrol car with a stolen transit van.