Investigators are working on evidence that the large hole that appeared in Stratford last week was caused by a network of 19th century wells.

Tunnelling work on a section of the £5.2bn Channel Tunnel rail link allegedly caused the subsidence and could raise third party liability issues, according to an industry expert.

"But the drilling company may have taken insurance for unforeseen ground conditions which would be within an errors and omissions (E&O) policy," said Marsh broker Andy Brown.