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Britain's first adder tunnels have been built to help the venomous reptiles cross the road, in a bid to boost their numbers after a decline in recent years.

The two trenches have a cattle grid-like grate on the top and are designed to allow sunlight in, as adders can't generate their own body heat.

A wildlife trust in Berkshire noticed the road - which runs through - was stopping two different populations of the species from mating.

is hoping other small mammals and reptiles will make use of the new crossing too.

Debbie Lewis, its head of ecology, says genetic mixing between the two different groups of adders is important.

"They are a part of our native biodiversity and could be extinct here in 10 to 15 years if we don’t do anything," she said.

The trust realised the road was a barrier for snakes after monitoring them with radio trackers. It became clear the adders were going close to the road but not crossing it.

(Vipera berus) are shy creatures covered in a distinct zig-zag pattern. The protected species lives in woodland, on heathland and moorland and has a good sense of smell. Cold blooded, they need the sun's heat to warm up and start hibernating in October - re-emerging in March.

A found that adders could disappear from the British countryside altogether by 2032. They can currently be found in England, Scotland, Wales but not in Northern Ireland.

Elsewhere, they can be found across Europe and Asia and even within the Arctic Circle.

So, how likely are you to see one if you live in Britain?

"They don’t like people so they’re more likely to disappear," said Mrs Lewis. "The chances of you seeing them are very slim. They can feel you approaching through the vibrations in the ground and are likely to stay away."

Although she said the public should still be cautious in the rare instance that they do see one, "they are venomous. Admire from a distance but don’t disturb them."

The says an adder bite is painful but "really only dangerous to the very young, ill or old." It says medical attention should always be sought immediately.

The last from an adder bite in the UK was in 1975.

The money to create the tunnels came from , which was set up 30 years ago to help native species under threat.

For now, the trust in Berkshire has to wait and see whether its plan is successful.

"The two populations weren’t mixing before so hopefully they will now," Mrs Lewis said. "It’s a bit of a trial as there are snake tunnels in other countries but not in the UK, this is the first one."