Twenty Devon homes have been evacuated after the discovery of old copper mines near the buildings.

The uncharted workings were found under the Ministry of Defence (MoD) estate at Horrabridge in south-west Dartmoor.

Affected families are being rehoused, while MoD engineers investigate.

Residents in other parts of the estate say they now fear for their children's safety.

You don't want to let children out of you sight - you wonder whether a hole is going to open up

Navy wife

The first 700-foot shaft was discovered a year ago under a couple's sitting room, after they were alerted by subsidence at their bungalow.

A second hole appeared 200 yards away in May.

Now a third has forced armed forces families out of their homes.

Two MoD houses are ringed by security fencing, and the MoD believes others will be affected.

Unstable ground

Twenty of the 30 houses in Chichester Close, worth about �120,000 each, are now empty.

One Navy wife, who would not be named, said: 'It's a worrying time.

Old maps have been proven untrustworthy

"A few of us have been told we can stay.

"But it's not reassuring to see big metal fences around empty houses with 'Keep Out - Unstable Ground' notices plastered about the place.

"You don't want to let children out of your sight.

"It sounds ridiculous but you wonder whether a hole is going to open up."

An MoD spokesman said inaccurate mining records showed the first shaft was sunk 500 metres away from the bungalow.

'Major problem'

"It is a major problem for us," he said.

"At Horrabridge we are looking for workings below our estate which aren't supposed to be there."

Residents fear for their children's safety

Professor Roger Burt of Exeter University said: "It was a problem for the miners themselves who would often break through into old flooded workings."

South-west Dartmoor is littered with old mines, some dating back to the Dark Ages.

Tin production began on the moor early in the 15th Century, continuing until 1750.

Copper and arsenic mining reached its height between 1700 and 1850.

Horrabridge was the site of the major Wheal Franco mine sunk in the 1820s.