BRITAIN’S biggest meteorite crater has been unearthed off the coast of north-west Scotland.

Spanning 25 miles, it was created 1.2 billion years ago by a 13bn-tonne space rock that crashed near present-day Ullapool.

When it struck the Earth, travelling at more than 40,000mph, its 1km diameter impacted the land with the force of 940 million Hiroshima bombs.

Scientists discovered evidence of the ancient strike 11 years ago, but have only just pinpointed its precise location beneath the North Atlantic.

It lies under the Minch, the rough sea separating Lewis in the Outer Hebrides from the Highlands on the mainland.

The crater is buried beneath both water and younger rocks between 15 and 20km west of a remote part of the beach.

Dr Ken Amor, an Earth scientist at the University of Oxford and lead author of the discovery, said: “The material excavated during a giant meteorite impact is rarely preserved on Earth, because it is rapidly eroded, so this is a really exciting discovery.

“It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.

“The next step will be a detailed geophysical survey in our target area of the Minch Basin.”

He first found debris believed to be from the collision in 2008, working with colleagues at the University of Aberdeen.

The exact site remained a mystery, but the thickness and extent of the deposit suggested it was near the coast.

The impact would have melted rocks and thrown up an enormous cloud of vapour, scattering material over a large part of the region around Ullapool.

Evidence was preserved by sandstone rapidly burying the crater.

Researchers discovered the spot by mapping the direction the meteorite material took at several different locations.

Published in the Journal of the Geological Society, the study was based on field observations, the distribution of broken rock fragments and the alignment of magnetic particles.

Unusual rock formations in the area were previously thought to have been formed by volcanic eruptions, but Dr Amor found evidence of a phenomenon known as “ejecta blanket”.

This represents debris thrown out when a huge object slams into the ground, in this case scattering its material over an area about 50km across.

Dr Amor said: “It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area.”

At the time, Scotland would have been close to the equator and had a semi-arid environment, and most life was still in the oceans.

The landscape would have looked a bit like Mars when it had water on its surface, and may have suffered a higher rate of meteorite impacts, colliding with debris left over from the formation of the solar system.

It is thought collisions with an object this size occur between once every 100,000 years to once every million years, but estimates vary because craters are obliterated by erosion, burial and plate tectonics, making it difficult to know our record of large impacts.

Smaller impacts, where meteorites are only a few metres across, are relatively common, happening once every 25 years on average.

The largest crater made by a meteor or comet was discovered in the Australian outback four years ago.