More than half of UK species have suffered declines in recent years and 15% are at risk of vanishing from our shores, a report has warned.
Intensive agriculture's "overwhelmingly negative" impact on nature has helped drive the declines, while climate change, loss of habitat and urban sprawl are also having an effect, the second State of Nature report said.
The study, which pools knowledge from 53 wildlife organisations, shows that 56% of almost 4,000 studied land and freshwater species suffered declines in numbers or areas where they are found between 1970 and 2013.
Declines have continued in this century, with 53% of species witnessing falls between 2002 and 2013, and there is little evidence to suggest the rate of loss is slowing down.
An assessment of 8,000 species shows that 1,199 species are at risk of disappearing from Great Britain, the report said.
Farming is key to what is happening, with more intensive agriculture affecting nearly half of the species studied and responsible for nearly a quarter of the total impact on wildlife.
A loss of mixed farms, changes to sowing patterns, a switch from hay to silage in pastures, increased use of pesticides and fertilisers and a loss of habitat such as hedgerows and ponds have taken their toll.
The report said government farming policies had led to dramatic changes in farming practices, almost doubling wheat and milk yields since the 1970s, but often at the expense of nature by disrupting the food sources and habitats species rely on.
While wood pigeons have prospered from a switch to autumn sowing which has provided more reliable winter food, the loss of ponds has hit great crested newts and increased herbicides have caused a huge decline in corn marigolds.
And pointing to the loss of 97% of wildflower meadows since the Second World War, Dr Trevor Dines, of Plantlife, said: "Where there were once flowers at our feet there is now a factory floor, little more than green concrete."
The report comes as the debate over the future of subsidies for farming after Brexit intensifies, with calls for future payments to focus on protecting wildlife in the countryside.
Climate change is also increasingly affecting UK nature although the impacts are mixed, with some species spreading north or surviving better in warmer winters, but others hit by loss of coastal habitat, increased sea temperature and wilder weather.
In the long term, global warming poses one of the greatest threats to nature around the world, the report warned.
In the UK, wildlife is also being hit by urban development on heathland and loss of town green areas and brownfield sites, changes to the way land and forests are managed, the draining of upland bogs and lowland fens and over-abstraction of water.
But elsewhere, the creation of new wetland by conservation schemes or in sites such as old gravel works and the planting of new woodland, as well as wildlife-friendly farming schemes, are providing habitats for struggling species.
Reintroductions of species such as the pine marten and large blue butterflies are also helping, but more needs to be done, the report said.
It follows on from the first State of Nature study in 2013, which sounded the alarm for the UK's wildlife.
Naturalist and TV presenter Sir David Attenborough said: "The natural world is in serious trouble and it needs our help as never before.
"The rallying call issued after the State of Nature report in 2013 has promoted exciting and innovative conservation projects.
"Landscapes are being restored, special places defended, struggling species being saved and brought back. But we need to build significantly on this progress if we are to provide a bright future for nature and for people.
"The future of nature is under threat and we must work together, governments, conservationists, businesses and individuals, to help it.
"Millions of people in the UK care very passionately about nature and the environment and I believe that we can work together to turn around the fortunes of wildlife."
National Farmers' Union (NFU) vice president Guy Smith argued that agriculture had not become more intense since the 1990s and questioned the suggestion it was responsible for the declines in the last quarter of a century.
Other factors such as climate change and urbanisation needed greater attention, he said.
And he said: "The NFU believes the sustainable intensification of agriculture will be an important tool with which farmers will help to make a significant contribution to the challenge of both domestic and global food security."
He said this meant using measures to enhance yields and promote better use of resources, such as precision application of fertilisers or fine-tuning livestock diets to reduce waste in the system.
"Good husbandry, good animal welfare and good agronomy all play a major role in balancing the need to produce food using less. This is why farmers are best-placed to be part of the solution.
"Above all we need to remember farming is here to provide one of the fundamental staples to life: food," he said.
A spokeswoman for the Environment Department (Defra) said: "Our natural environment is cleaner and healthier than at any time since the industrial revolution - woodland cover in England is at its highest level since the 14th century, we have improved water quality in 9,000 miles of rivers since 2010 and in the last five years almost 19,000 miles of hedgerow have been planted.
"Protecting our precious environment and supporting our world-leading farmers, a cornerstone of our economy, will form an important part of our EU exit negotiations.
"We will work to deliver the best possible outcome for the British people."