The system will cool a new nuclear power station being built at Hinkley Point in Somerset

It has been described as a giant plughole under the sea, sucking in 130,000 litres of water a second along with vast numbers of fish.

The twin inlet tunnels stretching two miles out into the Severn estuary are so big that a double-decker bus could drive through them. The system will cool a new nuclear power station being built at Hinkley Point in Somerset but conservation groups say it will kill up to 250,000 fish a day and must be altered or scrapped.

They say that EDF, the French state-owned energy group, has grossly underestimated the system’s impact on marine life in the estuary, a special conservation area.

A 5mm mesh will be installed to prevent larger fish being swallowed but the groups, including the