What are sinkholes, how are they formed and why did one appear in a Surrey street?

Failed water main or mineshaft most likely culprits as hole opens up in the village of Godstone

Residents of Godstone in Surrey have been evacuated from their homes amid fears that two large sinkholes in their high street could trigger a gas explosion. Here we look at what causes sinkholes, whether they are becoming more common and what can be done to prevent them.