The native adder is effectively disappearing from our landscape, a study has revealed.
The first nationwide survey of UK amphibian and reptiles has found that Britain's most widespread snake, the adder, is in decline.
Slow worms, common lizards and grass snakes are also becoming less widespread, as are the common toad, common frog and the great crested newt.
The only species found to be increasing its range is the palmate newt.
Dr John Wilkinson explains how to spot a common toad
These startling trends come from a report produced by the Amphibian and Reptile Conservation (ARC) Trust, which has been gathering data on 12 species since 2007.
The trust's National Amphibian and Reptile Recording Scheme (NARRS) has presented its interim findings, which cover the first half of the six-year survey period from 2007 to 2012.
The full survey aims to establish baselines for widespread species - figures against which future status changes can be assessed.
The survey focuses on widespread amphibian and reptile population. These include the great crested, smooth and palmate newts, common toad and frog, common lizard, slow-worm, grass snake and adder, as well as the wall and green lizards and agile frog in Jersey.
The rarest species, such as the great crested newt, already have high levels of protection, but it is strongly suspected that some formerly common species now in decline.
For this reason, the UK government passed legislation in 2007 prioritising the protection of common toads and all UK reptiles.
But this survey suggests that their numbers continue to fall.
Out of approximately 250 square kilometres surveyed, adders were found in about 20.
Our reptiles and amphibians are doing poorly, adders in particular are of concern
"Though we suspected that adders were getting much less common, it is very alarming that they turn up in only 7% of reptile surveys nationally," Dr John Wilkinson, Research and Monitoring Officer for the Amphibian and Reptile Conservation Trust, told BBC News.
"Adder occupancy is poor everywhere, making them our rarest widespread reptile by far and in need of serious conservation attention."
Historically, it was believed that adders were most at risk from persecution - people killing the snakes because they are venomous. But the ARC Trust say that their decline may also be caused by development and disturbance.
Other widespread amphibians and reptiles also appear to be in trouble.
"There is no single trend as different species are sensitive to different issues," explained Dr Wilkinson.
"Broadly, though, our reptiles and amphibians are doing poorly and adders in particular."
Common frogs are becoming less common in the south of England, particularly in areas which have experienced the most development in recent decades.
And, in the same area of England, the common toad is only half as widespread as the common frog.
"Great crested newts may be much rarer in Scotland than we thought - they haven't turned up in any of our NARRS surveys [there]," said Dr Wilkinson.
Common lizards, thought to occur throughout the UK, were seen rarely in the north and central regions, including Wales. Slow-worms were also found to be scarce in these areas.
Dr Wilkinson believes that this may be because these leg-less lizards are more difficult to find, as they burrow in undergrowth. So a reduced number of sightings may not necessarily reflect a decrease in their population
Surprisingly, palmate newt numbers are higher than expected, which might indicate changes in the quality of Britain's ponds.
Unlike many other amphibian species, these small newts thrive in acidic pools that are formed through acid rain fall or agricultural run-off.
The main drive of amphibian and reptile decline is thought to be habitat fragmentation and development.
Conservationists say this is a particular problem for toads, which are more sensitive than frogs to changes in habitat.
The final NARRS report is due to be published in Spring 2014.