The estuary has the second highest tidal range in the world and harnessing this could provide up to 5% of the UK’s electricity needs.

The proposed barrage would run from Brean, south of Weston-super-Mare, to Lavernock Point, south of Penarth near Cardiff. It would create a massive non-tidal lagoon inland of these points; ideal for watersports and other leisure pursuits.

The barrage would also transform coastal resorts like Weston and Burnham where visitors are used to seeing the sea disappear at low tide.

At least one large sea lock would be required to provide access for ships to major ports like Cardiff, Newport and Avonmouth and also for seagoing pleasure craft.

The beneficial effect on boating and navigation would be considerable, with connecting river estuaries like the Bristol Avon and the Wye also becoming semi-tidal, creating relatively easy passages between waterway entrances, harbours and popular marina locations such as Sharpness, Lydney, Bristol, Chepstow, Cardiff, Newport, Penarth and Portishead.

Construction of the barrage would, however, have a major impact on the environment and wildlife habitats of the estuary and on the lives of people living and working around it.

So – despite the advantages - there is likely to be considerable opposition to the proposal.