Fungi thieves are operating on an "industrial scale" in Epping Forest, according to the authorities.

This year, forest keepers issued hundreds of verbal warnings and an 'all-time high' 20 prosecutions, which resulted in average fines of £230 for offenders.

Epping Forest has 1,600 fungi species, including the oak polyphore, pink waxcap and sandy stilt puffball.

They are protected by the Wildlife & Countryside Act of 1981, making picking illegal.

The commercial thiefts can be highly dangerous because Epping Forest is home to the potentially fatal death cap and the destroying angel species of mushrooms.

Nonetheless, a spokesman for City of London said mushroom picking has become a "huge commercial operation".

John Park said:"We stopped a woman last year who had five carrier bags stuffed to breaking point with all kinds of mushrooms.

"She had come up from London on the Tube and had picked them for to sell at markets.

"It is now a major problem for urban green space providers."

Paul Thomson, Epping Forest superintendent, said on recent prosecutions: "These people were caught picking mushrooms in prodigious quantities with large double bags full of them.

“Most people listen to us and stop but some of the people we met were clearly picking commercially.

“When they got back to their vehicles their whole boot was full."

Epping Forest gets 4.5 million visits a year, and is London and Essex’s biggest green space but foraging is impacting on the woodland’s biodiversity by breaking the forest’s natural processes of decay and renewal.