An expensive Mediterranean black truffle has been cultivated in the UK for the first time, the farthest north that the species has been found.

Researchers believe the truffle, mostly found in northern Spain, southern France and northern Italy, was able to grow in Wales due to climate change.

It was grown in Monmouthshire as part of a project run by truffle firm Mycorrhizal Systems Ltd (MSL) and it was harvested in March 2017 by a trained dog named Bella.

The aromatic fungus was growing within the root system of a Mediterranean oak tree that was planted in 2008 and treated to encourage truffle production.

It had been inoculated with truffle spores, and the surrounding soil was made less acidic by treating it with lime.

Further microscopic and genetic analysis confirmed that Bella's find was a Perigord black truffle (Tuber melanosporum).

Dr Paul Thomas, of MSL and the University of Stirling, said: "This cultivation has shown that the climatic tolerance of truffles is much broader than previously thought, but it's likely that it's only possible because of climate change, and some areas of the UK - including the area around Cambridge - are now suitable for the cultivation of this species."

The black truffle is one of the world's most expensive ingredients, worth as much as £1,700 per kilogram, but its Mediterranean habitat has been affected by drought due to long-term climate change, and yields are falling while the global demand continues to rise.

"This is one of the best flavoured truffle species in the world and the potential for industry is huge," said Dr Thomas.

"We planted the trees just to monitor their survival, but we never thought this Mediterranean species could actually grow in the UK - it's an incredibly exciting development."

A study by the firm, together with Cambridge University, has been published in the journal Climate Research and suggests that truffle cultivation may be possible in many parts of the UK.

But Professor Ulf Buntgen of Cambridge's Department of Geography said: "It's a risky investment for farmers - even though humans have been eating truffles for centuries, we know remarkably little about how they grow and how they interact with their host trees."

The first truffle to be cultivated in the UK was a burgundy truffle in Leicestershire in 2015.

This is the first time the more valuable black Perigord truffle has been cultivated in such a northern and maritime climate.

The first harvested truffle, which weighed 16 grams, has been preserved for posterity, but in future, the truffles will be distributed to restaurants in the UK.