The wet summer may not have suited everyone but Britain's truffle hunters are delighted. They are predicting a bumper crop of the fungi known as “black diamonds”, over which gourmets go into rhapsodies.

A chilly spring followed by sunshine and then summer rain has created perfect growing conditions for the pungent delicacy. The British summer truffle may not be as highly regarded by epicures as the French and Italian varieties, but it is still worth about £180 a kilo.

One couple from Plymouth were celebrating yesterday after their gardener discovered truffles worth hundreds of pounds growing between the roots of beech trees in their garden.

However, a plantation at a secret location in Wiltshire has become one of the world's most productive sources of British summer truffles. The three-hectare (7-acre) site produced 200kg (440lb) of the delicacy last year, and an even bigger harvest is expected this summer.

The truffle expert Nigel Hadden-Paton, the first Briton to be invited to join the Confrérie de la Truffe de Bourgogne, France's leading truffle “brotherhood”, said: “No one has seen anything like it. The quantity of truffles is simply astonishing.We have found them up to 500g [17oz] each, which means they are bigger than cricket balls.”

Truffle spores are believed to have been imported to Wiltshire in the roots of beech, oak and hazel trees planted 12 years ago. The slightly acidic soil proved the perfect growing medium — last year's harvest was worth about £27,000.

Traditionally pigs were used to root out truffles in the Périgord region of France, although dogs are increasingly used.

But the Wiltshire farmer, who does not want to be identified for fear of attracting hordes of uninvited truffle hunters, has his own unorthodox method, according to Mr Hadden-Paton.

He said: “He finds them by taking off his shoes and socks and feeling around with his feet.”This year's truffle season is likely to be relatively short because the damp conditions which helped them grow will also rot them unless they are harvested quickly.

Chris Hunt, 47, a gardener in Plymouth, was clearing undergrowth from around some beech trees for an elderly couple when he discovered more than two kilos of truffles, worth several hundred pounds. Mr Hunt said that neither he nor the owners had any idea that the truffles were growing there. He said: “The area hadn't been cleared for a long time because the people who live there are physically unable to do it. We came across a fairly large truffle, about seven to eight centimetres long, and as we carried on working we found about nine to ten more.”

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