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The new footage shows how the chain that the trawlers drag behind them scours the seafloor, forcing the creatures it disturbs into the net behind.

By looking at the changing scratch marks on the seafloor, the researchers discovered an abrupt shift in Britain's icebergs about 18,000 years ago, a time when the planet was gradually warming from a very cold period.

This is a bit like doing an MRI scan of the sediment layers beneath the present-day seafloor, going back millions of years.

It's also a remarkable feat of engineering, that will see segments of the tunnel placed on top of the seafloor, and then joined together.

Next it's a painstakingly complex procedure, lowering the elements 40 metres down into a trench dug out on the seafloor, using underwater cameras and GPS-guided equipment, to line it up with 15mm precision.