It is expected to reveal the less salubrious parts of Roman London outside of the City walls with archaeologists anticipating to encounter Roman timber-framed buildings and a street surface 6m below ground level.

BBC: Crossrail dig unearths forgotten London

"The controls we had put in place were inadequate due to the unusually high rainfall, which resulted in surface water flowing onto a track that was being used by heavy machinery to extract timber from the forest, " added Mr Garson.

BBC: Forestry Commission fined ?24,000 for Powys pollution