Thames Water engineers will inspect every part of the machine over the next two weeks at Germany’s Herrenknecht factory before the TBM is broken up again to transport.

The 100m long TBM will be shipped to Tilbury next month to be reassembled at Beckton sewage works where preparations are made to start tunnelling 70m below ground.

Tunnelling work on the £639m Lee Tunnel is due to begin in January and  finish in late 2013.  The machine is likely to creep along at a rate of 17m a day.

The largest part of the machine is an 8m diameter cutting head, which will be transported in four parts.

“Tunnelling is a risky business, especially on this scale,” said Thames Water’s Lawrence Gosden.

“We face the challenge of boring the deepest tunnel in London at some of the highest groundwater pressures that a machine of this type has tunnelled in, drilling through four miles of the most abrasive ground without any shafts along the way.”

Its aim is to prevent 16m tonnes of sewage entering the Lea river each year, resulting from London’s Victorian sewers not being big enough any more to cope with urban expansion and heavy rainfall.