The explosive secret of Britain's mines

Until about 40 years ago, mining had been going on beneath the Forest of Gwydyr since the Bronze Age. Today, the only signs visible above ground are a handful of derelict buildings. But concealed within the labyrinth below, where men toiled in the dark in search of zinc and lead, lies a truly explosive secret.

A huge cache of abandoned dynamite has been discovered in one of the deepest mines in the North Wales forest. The explosives, hastily abandoned when the mines were closed in the 1950s and 60s, and now highly unstable, have been left where they lay to rot, surrounded by newspapers dropped by the last miners as they finished their final shift. One mine alone is estimated to have up to 250 sticks of dynamite still inside.

The explosive power could still cause a lot of damage, said Robin Murray, a local fireman and cave rescue specialist. "There have been incidents in the past where some have gone off," he explained. "They are highly susceptible to radio signals and sparks because as they decompose they become highly unstable. If this lot went up it would certainly cause a hell of a big hole in the ground."

There are nearly 100 miles of workings beneath the forest where, at the peak of production in the 19th century, hundreds of men were employed bringing lead, zinc, silver or arsenic to the surface to supply the workshops of Britain's industrial revolution. Dynamite was used to blast the granite rock where the minerals were found.

Today, tracts of the inner workings, spread over many levels, are flooded, badly decayed and dangerous to all but the most determined and skilled cavers. Inquisitive walkers are strongly advised to keep out as crumbling floors conceal drops of up to 150ft.

The first modern, industrial-scale mining began when Sir John Wynn of Gwydyr started workings at sites such as Gwaynllifion around 1607. By the mid-19th century large quantities were being extracted from Hafna, Vale of Conway, Llanrwst, Coed Mawr Pool and Parc mines. As prices fell and mines dried up, some became fronts for the unscrupulous to trick London investors out of their cash. One scam involved painting the interior of a mine silver to convince a group of investors it was viable.

Today, there's talk of reopening some sites in response to soaring commodity prices. Meanwhile, visitors can enjoy the spectacular scenery of the undulating plateau, with its views of Snowdon, as they walk the Gwydyr Forest Park Miners Trail taking in the best preserved of the old workings.