The unidentified creature has been discovered living in plane trees in the museum's own gardens.

It is almond-shaped, red and black and about the size of a grain of rice.

While the bug is harmless, experts say it has the potential to spread throughout Britain.

It was first spotted in March last year, and in five months became the most common insect in the museum's wildlife garden.

One of the centre's insect experts Max Barclay said: "It seems strange that so many of these bugs should suddenly appear.

"With international trade and climate change, several new insects are showing up in London every year. Some of the invaders come from southern Europe, but others are from as far away as Australia. The fauna of the city is changing all the time now."

Museum staff have scoured their 28 million specimens and found no exact match for the insect.

However, experts at the National Museum in Prague say it matches their specimen Arocatus Roeselii - a bug which normally lives in Central Europe on alder trees and is usually brighter red.

Mr Barclay said: "There are two possible explanations. That the bug is Roeselii and by switching to feed on the plane trees it could suddenly become more abundant, successful and invasive. The other possibility is that the insect in our grounds may not be Roeselii at all."

The Museum is now continuing research on the insect's body shape and DNA to determine what it is.

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