Following the breakthrough at Paull on 10 September, the TBM was dismantled and lifted to the surface ready to be shipped back to Germany to be fully refurbished ready for her next tunnelling challenge.

For the last 18 months, she has been steadily making her way from Goxhill on the south side of the river to Paull on the north bank, constructing a tunnel nearly 5km long and 3.65m in diameter, ready to carry a vital pipeline which can provide up to a quarter of Britain's gas supplies.

During Mary's journey under the Humber, approximately 160,000t of material were excavated - mostly chalk, which has been carefully transported back to the surface, graded and re-processed at the Goxhill slurry treatment plant. The excavated material is being used to help restore a former quarry nearby.

Steve Ellison, lead project manager, Capital Delivery, for National Grid, said: "Completing the tunnel beneath the Humber is a major milestone for the project team and our project partners. It's the first time a tunnel has been constructed beneath the River Humber and a fantastic achievement for everyone involved.

When one pipe section has been installed, the next will be moved into position, welded to the one in front, and the push will continue until all 5km of pipeline is installed beneath the river. When complete it will be the longest hydraulically inserted pipe in the world.

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